Why is Buddhism less evangelical than Christianity?

This is 8 years late but I would like to offer another perspective. I agreed that Buddhists (at least those that I know of) are not very proactive or keen to proselytize. Partly, it is because the Dharma is hard to understand and it appeared that the Buddha himself was initially not keen to teach for this same reason. (Note: there are some disputes that the Brahma’s request to the Buddha to teach is a later addition as it is not found in the Mahayana version). But the fact that the Buddha initially thought of teaching his Dharma to his first teachers, Ālāra Kālāma and Uddaka Rāmaputta before settling on his five companions (and not anyone he sees), already showed his concerns that his teachings is hard to grasp.

My observation is that Buddhism tends to attract truth seekers i.e. people who are more interested in understanding reality. Therefore, it is no surprise that scientists and researchers are naturally attracted to Buddhism. Similarly, the Buddha’s intention was to share his discovery with the belief that anyone who followed his steps would likewise come to the same conclusion. This is, in a nutshell, the scientific method. The Dharma, therefore, represents a body of knowledge. Like all bodies of knowledge, there are many pieces that needed to fit together to see the whole picture and not everyone is naturally passionate to spend the time and effort to learn the pieces and fit them together.

My analogy would be someone approached a professor in Mathematics and requested to be taught calculus. The professor proceeded by explaining he needed to first teach the wannabe-student algebra followed by geometry and trigonometry. The student protested and insisted they just want to learn calculus, they were not interested in geometry or trigo and they already knew algebra. So, the professor tested the student on some algebraic questions and the student failed. The professor patiently pointed out that the student's understanding of algebra was wrong and lacking. At this point the student complained that the professor was a quack and walked away in anger.

Supposed an enthusiastic Buddhist approached some non-Buddhists to spread the Dharma. And he began by telling them their understanding of stress or suffering (dukkha) is wrong. I believed there will be a lot of disappointed or angry faces. The sad truth is most of the people in the world are not interested in reality. People are constantly looking for ways to twist reality to suit their hearts’ desires. If a religion declared that reality was created by an almighty god and that if they become followers even the laws of physics can be altered for them. That would be news that is instantly comforting and heartening to those who are struggling in their lives. Unfortunately, for Buddhists, who truly understand the Dharma, to make such a promise would be an outright lie. For this reason, there are not many who are receptive to the Buddha's message. Not many are willing to question their desires and investigate the reality behind their struggles in lives.

For the truth seekers, the words of the Buddha alone act as a mirror reflecting themselves. There is no need to brainwash anyone because there is no "self" to be rewarded. This is why I believe traditionally, there was never any need to proselytize in Buddhism. I hope fellow Buddhists will not be goaded into emulating the misguided ways of others by denigrating other religions just to proselytize. I hope we will continue to emulate the Buddha's approach. Speak the truth, lay out the facts and invite people to come and examine themselves, ehipassiko.

For the sake of salvation, Christianity is an easy religion of basic morals & faith. Jesus said:

Take my yoke upon you and learn from me, for I am gentle and humble in heart, and you will find rest for your souls.

Matthew 11:29

In Buddhism, attaining Nibbana requires the eradication of self-view, which is too difficult & even potentially psychological dangerous for most faith-follower Buddhists, let alone too difficult for most people. The Buddhism himself did not teach non-self/emptiness to most people.

Most Christians believe, based on Matthew 28:18-20, that they must spread Christ's message. In other words, if they don't do it, they aren't following Christ's instructions:

'Then Jesus came to them and said, “All authority in heaven and on earth has been given to me. Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you.'

And one possible reason Jesus himself gave that instruction was because the Christian view of existence is one where this human life is pretty much your one and only chance to get into heaven. If you screw up here, there's no rebirth, no time-limited lower realms, and not even simple extinction -- it's the Bad Fire and the Jaggy Stick Up The Bum Fandango, for eternity.

Obviously we can find some sense of urgency in Buddhism too: e.g. the illustration of practising as if one's hair was on fire. But nothing scares the bejeezus (literally) out of people the way the Christian notion of eternal perdition does.

Just so it's said, Christianity is effectively an 'all or nothing' faith. You're born, you live, you die, and then you go to heaven or you don't. Buddhism (in its original form) is a 'recycling' faith. You're born, you live, you die, and if you don't get it quite right you just go back around to the beginning and do it again.

Buddhists can afford to be more chill about it.

Is there something in the scriptures or teachings that make Buddhist less evangelical?

One thing is that Buddhist scripture has some emphasis on teaching 'skillfully'.

Some explanations of 'right speech' include the requirement that speech be beneficial, welcome, and at an appropriate time; for example:

The Abhaya Sutta elaborates:[34][35]

In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial, unendearing and disagreeable to others, he does not say them.

In the case of words that the Tathagata knows to be factual, true, yet unbeneficial, unendearing and disagreeable to others, he does not say them.

In the case of words that the Tathagata knows to be factual, true, beneficial, yet unendearing and disagreeable to others, he has a sense of the proper time for saying them.

In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial, yet endearing and agreeable to others, he does not say them.

In the case of words that the Tathagata knows to be factual, true, but unbeneficial, yet endearing and agreeable to others, he does not say them.

In the case of words that the Tathagata knows to be factual, true, beneficial, and endearing and agreeable to others, he has a sense of the proper time for saying them. Why is that? Because the Tathagata has sympathy for living beings.

In every case, if it is not true, beneficial nor timely, one is not to say it. The Buddha followed this, for example, when asked questions of a purely metaphysical nature, unrelated to the goal, path or discipline that he taught. When asked a question such as "Is the universe eternal?", the Buddha dismissed the topic with the response: "It does not further." (or: "The personal possibilities (goals) assigned you are not furthered by an answer to an ultimate question about the universe's fate.")

Conversely, "The gospel" is from a Greek word meaning "Good news": and the word "news" implies that it's meant to be broadcast? And the Christian Parable of the Sower seems to me to imply "broadcast" instead of "person-to-person" speech.

Currently when I walk to work I frequently pass Christians of various denominations passing out free books and talking to passers by. I have never heard of a Buddhist group doing the same.

To some extent some Buddhists do pass out free books: for example I picked up one free book by walking in to a Buddhist temple and looking in the book store.

I've also seen a "free book" left in a hotel room in Singapore (in the same way that you might find a "Gideon's Bible" there).