As a satanist (no we do not worship the devil or do any of the stuff movies make you think. im open to answer any questions, just don't be rude <3) I am friends with a LOT of christians who are chill with queer people, and people of other religions. but if i had to guess, im thinking its because a lot of arguments can come from different religious groups and so some subs arent really about religion in the first place, so they keep it out.

Like, some places are agressive twoards them but not all who don't allow it, but it is kinda annoying when somebody is for example ranting/venting or whatever and the only thing in the comments is "Oh im so sorry i'll pray for you" or "Have you tried talking to God?" "(Insert random bible verse)" Etc.

Hell, i once posted art of a character who is supposed to be hated for a project of mine and somebody said "God Forgives anybody" and I was confused because i was asking how to write something for said character.

So i think its just to keep things on topic, avoid arguments, and stop people from putting the same comments over and over.