Connor Wood, at Science on Religion:
Because ritual and conformance are easy.
There’s good evidence that atheism and secularism are much more costly, in terms of sheer energy expenditure, than religious ways of organizing society.
So is atheism a luxury of the wealthy? Yes. But this isn’t simply because the wealthy don’t need the comforts of a posited afterlife. It’s also because materially comfortable people have more energy to expend on negotiating their social worlds. Ritual and religion use intuition and demonstration; they prioritize efficiency and clarity of signals. Secularism uses logic and abstract reason; it’s comfortable with ambiguous social roles and signals. In part, this is because it can afford to be.
There’s also the idea that religion is easy, science is hard; I have a whole book on this theme I will read soon and blog upon. It’s easier to conform to your familial or social group, than to be independent and think for yourself.