In your opinion what causes christians to believe in Jesus

[Thumpalumpacus]

And when other faiths posit afterlives, do they promise an impossibly pleasurable Heaven?

I'm not sure Christianity has the most pleasurable heaven from a secular perspective. This is why I said earlier that for the Christian the appeal of heaven is Jesus, meaning you have to already have a belief and an interest in the person of Jesus to find heaven appealing.

Plenty of other religions have a much more exciting afterlife if all you care about is living long and not being too scared when you die.

(And btw, isn't it a common atheist argument that life would be boring and meaningless if it was eternal?)

Why are you expecting Christians to adopt an atheist argument? I'm making these points from a Christian perspective because that's what you asked for -- why Christians believe, not what I believe nor why. It's called trying to be objective. You should think of it as "for the sake of argument".

You're starting to appear disingenuous here.