Christianity

I like to imagine that there's no divinity or anything like that, it's just that the vast majority of vampires fucking detest christians for one reason or another, and simply refuse to stick around when they see a crucifix.
Some are so ancient that they spoke to mohammad and are devout muslims, some just predate christianity so consider it extremely stupid, some had bad experiences with the catholic church and don't care to distinguish sects, and some simply fell into the militant atheist rabbithole and unironically wear fedoras because obviously no one can stop them doing so.