Why are religious history questions so rare?

Because everyone is interested in trying to prove that their "god" exists. They just want to doll out scripture after meaningless scripture instead of having a logical conversation etc. Furthermore, a lot of real (as opposed to religious) history would certainly make people lose their faith and of course they avoid anything that would do that (including history, psychology, biology, evolution, anthropology, etc). Faith seems to be the trump card. And we all know you cant argue with faith. It's rather exhausting.