Why didn't Buddhism become Popular in India in Lord Buddha's time?

so my question is if budhism is very good religion why it didn't went all over the india, Why Buddhism not became Popular in India in Lord Buddha time?

Actually, the Buddha traveled extensively around the territory and he is said to have had the most followers along with the Ājīvikas and the Jains.

After his death, popularity increased much more, particularly with imperial support by Ashoka, who not only helped build monasteries and raising pillars with Buddhist ethics content around the empire, but also financed missions to spread Buddhism beyond.

Later on, though, Buddhism declined in India, presumably through many forces. Among them, I've seen:

• Lost (and lack) of support from royalty (later favoring Brahmanism).
• Buddhism persecution during the Shunga Empire.
• War and invasions (some of which destroyed buddhist universities, particularly big ones such as Nalanda).
• Schism within the buddhist sangha.
• Lack of engagement of monastics with laity (one of the criticism drawn in the Mahayana/Hinayana polemics).
• Socio-economical circumstances driving interest of the public to Brahamanism -- and ability of the latter to incorporate and mix buddhist elements.

During The Buddha's time, he was just another teacher in India, there were many others teachers and dhammas already existing in India.

I can't find the suttas detailing the number of followers The Buddha had during his time but probably still at least 10,000 (including lay followers).

In ancient times that's how things start off, they only become popular later on. The majority of people all around the world were illiterate prior to the 17th Century so transmitting information was done primarily orally and verbally.

Spreading ideas in ancient times was much more difficult, and still in modern times it would be difficult. Scientology for instance only gained popularity later on in time.

Christianity and many other religions also started off very small and only gained popularity much later on in time.

There are a few hypotheses to explain why Buddhism didn't gain popularity in India later on:

• Caste system (The Buddha was against it, seems to be only found in India or regions near India)
• Buddhism was never in India anymore popular than Jainism was in India (Jainism is also unpopular in India in modern times)
• Buddhism was prosecuted and forcefully exterminated from India
• Vedantist teachings lead to the decline of Buddhism in India

But in reality Buddhism still lives on in India since post-Buddhist Hinduism seems to have copied or integrated concepts from Buddhism, same with post-Buddhist Jainism.

It is also possible that Christianity was influenced by Buddhism since Buddhism was popular among the Greeks for some time.

I think the premise of your question is incorrect. During his lifetime the teachings of the Buddha were very popular, including amongst the mercantile classes and several kings, and after his life it spread across India. The reason for the subsequent disappearance of Buddhism in India is the Muslim invasions and also the subsequent success of Hinduism, which incorporated many Buddhist teachings but in a more populist form. Some scholars also think that the popularity of Tantra in later centuries weakened Buddhism.

Here's a nice detailed article on that:

DECLINE AND FALL OF BUDDHISM in India

To define popular in India in Lord Buddha's time would be hard ..as people were struggling to survive ( general masses ) ..and new thoughts of do nothing ...life is suffering etc were concepts only the mystics could adhere too .. Sometimes even today the messenger and message fall in deaf ears but sure enough when concerned with dharma / Buddhism it's about accepting the real state of life how many even today want to know this detail when there is so much else we could be doing .

There was an empire in India, which was at least partly Buddhist: https://en.wikipedia.org/wiki/Maurya_Empire

The emperor became Buddhist: https://en.wikipedia.org/wiki/Ashoka#Buddhist_conversion

According to Wikipedia, the Maurya Empire started in 320 BC; and Siddhartha Gautama died in about 400 BC plus or minus a few decades; so, that empire started (only) about 50 or 100 years after the Siddhartha Gautama's death.

The pilgrimage sites on the map you quoted are places associated with Siddhartha Gautama's life (after which, the "popularity" of Buddhism extended beyond those places).

Okay, let me start by saying I'm not a super religious person but having lived in Srilanka, right next to India and a Buddhist country qualifies me to answer this.

Indians at the time of Gautama Buddha were mostly Hindus and had a caste system where the Brahmans, the teachers of Hinduisms were on the top and the poor was at the very bottom. The poor literally had to jump in to the drains when people of higher castes were traveling on the same road. The Buddha, however, opposed the caste system and he was very ambiguous about the creator deity Brahmans and Eternal self Atman and rejected them both.

So, there were somewhat of a tension between hindu brahmins and buddhist monks. The Buddha however did not deny the existence of gods (devas) and said that the did exist in other worlds that is better than our world but are subjected to the same samsaric sufferings as humans. They too die but they have much larger life spans compared to us. Humans can go to these heavens if they do enough good deeds and when it runs out, they will be reborn depending on their karmas.

Buddhism attained prominence as it was supported by Royal courts and virtually disappeared from India after the fall of the Guptas. By the 8th century Shiva and Vishnu.

However, Emperor Ashoka who ruled most of India from Afghan mountains to Bangladesh was greatly responsible among other kings for spreading Buddhism around the world. He created Nalanda a huge library containing Buddhist documents and even some Hellenic people turned to Buddhism during his reign as well as Pakistan and Afghanistan. He sent his own son and daughter to Srilanka with a branch from the tree that the Buddha attained Nibbana and ordained the king and the royal court at the time.

Troops from the Muslim Malmuk Dynasty later destroyed Nalanda, along with a huge number of Buddhist scriptures and eventually the Boh tree the Buddha attained enlightenment was cut down. The one in Srilanka is still there and is the oldest tree in the island. Events like these and Hinduism coming back to the royal courts gradually decreased the number of Buddhist followers in India.