Why is Buddhism a venture of a limited few?

Every single one of these answers looks at the issue from the Buddhist perspective, rather than an average human being perspective. Furthermore, most of the answers try to denigrate those not taking up Buddhism, to comparatively increase their own self-worth (so much for compassion and empathy).

The hard facts are these:

1. The Buddha was a spoiled rich boy that got bored and left his castle.
2. He saw that most people had horrible lives and had absolutely no way to make their lives better (ancient India, caste system, etc)
3. The alternatives, at the time, were: suffering, Buddhism, or suicide.

At the time, Buddhism seemed like a reasonable choice.

Now, life on average is a little bit better, and it's easy to have delusions of grandeur, so there is a valid alternative to letting go of all ambitions.

The truth is that it's the same reason why most people don't become monks. In fact, with religion, there is the idea of heaven. With Buddhism (raw and true Buddhism) there is no such thing, there is just - "you feel and want nothing and then you die."

I know for a fact that this will be taken as trolling, but Buddhism before the 4 schools (5 if you count the silly Nyingma wizards) made a ton of things up was just the 4 noble truths and the eightfold path. It's stoicism in a different wrapper, nothing more.

My question is if Buddhist understanding of human condition and psychology is true why only limited few humans want or strive towards Nirvana.

People identify with their suffering.

My question is if Buddhist understanding of human condition and psychology is true why only limited few humans want or strive towards Nirvana. If Buddhist cosmology is true why not humans enmasse on the Buddhist path?

Because of a disease called the Four Perversions every single one of us un-enlightened earthling is afflicted with to a greater or lesser extent:

“Monks, there are these four perversions of perception, perversions of mind, perversions of view. Which four? ‘Constant’ with regard to the inconstant is a perversion of perception, a perversion of mind, a perversion of view. ‘Pleasant’ with regard to the stressful… ‘Self’ with regard to not-self… ‘Attractive’ with regard to the unattractive is a perversion of perception, a perversion of mind, a perversion of view. These are the four perversions of perception, perversions of mind, perversions of view." ~~ AN 4.49 ~~

I think one either experiences a lot of stress or is able to appreciate the stress experienced by others very intensely. This makes one life & death kind of serious. Some people experience a lot of hardship and don't get wiser tho.

It's extremely difficult to let go of sensual enjoyment. Experiencing sensual enjoyment leads to clinging, meaning trying to experience even more sensual enjoyment.

Hence, the masses have the natural tendency towards burning with sensual fever, rather than trying to escape it. It's a vicious cycle.

From Magandiya Sutta:

"Now suppose that there was a leper covered with sores & infections, devoured by worms, picking the scabs off the openings of his wounds with his nails, cauterizing his body over a pit of glowing embers. The more he cauterized his body over the pit of glowing embers, the more disgusting, foul-smelling, & putrid the openings of his wounds would become, and yet he would feel a modicum of enjoyment & satisfaction because of the itchiness of his wounds. In the same way, beings not free from passion for sensual pleasures — devoured by sensual craving, burning with sensual fever — indulge in sensual pleasures. The more they indulge in sensual pleasures, the more their sensual craving increases and the more they burn with sensual fever, and yet they feel a modicum of enjoyment & satisfaction dependent on the five strings of sensuality.

There's also another vicious cycle.

According to MN 9 (below), as long as you still have fermentation or effluents, you would still have ignorance, and vice versa (also see this question). Ignorance is a very deeply ingrained and deeply lingering fetter.

From the origination of fermentation comes the origination of ignorance. From the cessation of fermentation comes the cessation of ignorance. .....

From the origination of ignorance comes the origination of fermentation. From the cessation of ignorance comes the cessation of fermentation.

There is a vicious cycle between ignorance and fermentation.

It's very hard to escape these. Natural evolution sustains these vicious cycles.

OP: My question is if Buddhist understanding of human condition and psychology is true why only limited few humans want or strive towards Nirvana. If Buddhist cosmology is true why not humans enmasse on the Buddhist path?

Actually Tathagata saw this and mentioned it in many occasions. We can find plenty of phrases in Pali canon which emphasise that only few people understand this subtle and deep Dhamma and get across this Samsara.

"Appaka te manussesu
ye jana paragamino
athayam itara paja
tiramevanudhavati"
~ Verse 85, Dhammapada

Meaning: Few among men reach the other shore (Nibbana); all the others only run up and down on this shore.

"Ye ca kho sammadakkhate
dhamme dhammanuvattino
te jana paramessanti
maccudheyyam3 suduttaram"
~ Verse 86, Dhammapada

Meaning: But those who practise according to the well-expounded Dhamma will reach the other shore (Nibbana), having passed the realm of Death (i.e., samsara), very difficult as it is to cross.

Tathagata has never told a lie. This Dhamma is true irrespective of the time period. So the following should also be true for past, present and future:

"Appamadena Bhikkhave Sampadetha
Buddhuppado dullabho lokasamim
Manussattabhavo dullabho
Dullabha Saddhasampatti
Pabbajjitabhavo dullabho
Saddhammassavanam dullabam"

Meaning: Oh, Bhikkhus! Strive on with diligence. Rare to appear is the Enlightened One in the world. Rare is it to be born as a human being. Rare is it to be endowed with the conviction in the three Gems, Kamma and its result. Rare is it to attain the bhikkhuhood. Rare is it to hear the Teaching of the Buddha.

From above quotes, you can understand why only limited few humans want or strive towards Nirvana.

Note: This is how I understood. I may be wrong but not Dhamma.

For something to mature there must a state of not being mature. Most beings are not mature in their faculties and accumulated merit, many beings are humans not enjoying the accumulated merits much, they are not rich, they are not well-off but they have opportunity to do a lot of good deeds and by the merit of those deeds attain a better state; there are also those who are' living of the previously accumulated merit, enjoying sensual pleasures much and are well-off. Very few are ready to turn away from both merit and demerit, most are longing for what they don't get enough of and what is considered difficult to attain.

Only a few centuries ago people had no idea about hygiene. There was simply no idea that dirty hands, filthy surfaces etc. was a good environment for growth of bacteria causing diseases.

Only a century or two ago (depending on country) there were no public schools. There was no common understanding that children require systematic education in language, mathematics, and sciences.

Only 50 years ago there was no notion of healthy lifestyle. The virtue of healthy natural diet and exercise was virtually unknown to the wide population.

Only 30 years ago the scale of human impact on planet's ecology was not understood at all. Humans were completely careless about pollution and overconsumption of natural resources.

Similarly, the real science of sentient ethics is not yet understood by humanity. There is no understanding of conceptual mind, how it develops, how it builds its picture of the world and the self, how this picture leads to actions, and how this creates experience of happiness or suffering.

Happiness is not really understood. Suffering is not really understood. Mind is not really understood. What's good and what's bad is not really understood.

Since people don't understand happiness, suffering, mind - they are confused about what is really important. They get fooled by the fake shiny promises of the materialistic civilization. They pursue things they were told will make them happy. But as they do that they only end up creating even more trouble for themselves because they don't understand how things work. They keep spinning in this vicious cycle of trouble, confusion, fake promises of happiness, and wrong action causing more trouble. They think they have no time to stop and look around. They don't know any other way to live. It really is very sad.

At some point humanity will evolve to understand these concepts, and then the things that Buddha taught will be common knowledge taken for granted, just like hygiene, public education, healthy lifestyle, and ecology are taken for granted today.

The question you asked is Why. Why are people ignorant of how mind works? Because self-reflection and self-awareness is hard. It's much easier to study the external world. Most people don't have enough motivation to study the external, let alone the internal which is much harder to understand.

Why don't people have motivation? Because they don't see the reward, they don't see how studying mind can help them achieve their goals.

Perhaps they have wrong goals you'll say - and I will agree, most people pursue all kinds of superficial goals they adopt out of ignorance.

As Buddha explained, ignorance is innate. The mind is a recognition and interpretation machine. It recognizes signs and interprets them to their meanings. The tremendously complex system of signs and their meanings is our model of the world, model of reality. This model is rebuilt by each generation based on the information passed on by the previous generations. The way this model is constructed starts from the superficial observations and gradually moves to deeper realizations.

Children are superficial, their minds are superficial, their understanding of life is superficial - because they are just starting out. Similarly, most people are superficial about mind, and happiness vs suffering, and ethics (what goals are worth pursuing). Why? Because it's deep, it's not obvious, it's not easy to see. And because other things that are easy to see completely absorb their attention.

From a separate perspective, simply looking at humanity and how people function, I'll point out that practicing Buddhism in the way needed to reach nibbana is work. Throughout history, humans show an aversion to work: we are naturally lazy.

Even outside of Buddhism, people stray from the paths of their religions.

• We see similar problems in mainstream Christianity. Jesus's main rule is, "love one another as you love yourselves." Yet, despite it's complete simplicity, many (most?) self-professed Christians routinely exhibit non-loving behavior and attitudes towards others. Maintaining a consistently loving approach to everyone and everything, all the time, is work. And, again, we're lazy.

• We see similar problems in mainstream Judaism. Tikkun olam, or "fixing the world", is a fundamental tenet: the basic idea is that the world is broken, and we humans must endeavor to fix it. Put another way, we should leave the world better than we found it. Yet, despite the simplicity of this dictum, many (most?) self-professed Jews routinely engage in behaviors and attitudes that don't improve the world. Maintaining a consistently constructive approach to everyone and everything, all the time, is work. And, again, we're lazy.

(I am personally unfamiliar with Islam, Hinduism, etc., so I will not make any similar comparisons here, although I suspect they could be made.)