SarahC:

Why do you think that is?

Well, as I said, that question is very hard to answer not only because it's complex and involves many concepts that aren't amenable to a no-nonsense scientific approach, but also because any sensible answer must include ideologically sensitive claims. History of ideas is a fascinating subject, but also an extraordinarily difficult one.

I don't have anything like a complete and plausible theory that would answer your question, but one thing of which I am certain is that such a theory should start with re-examining the standard notion of "religion," which I believe has outlived its usefulness in the modern world, and is nowadays creating more confusion than insight. But getting even just into that topic means opening enormous cans of worms.