Why do vampires always attack Christians?”
First this all being fictional or myth, as in not true, vampires do not really attack anyone. They are not real and the Christians are not real. Second within the structure of the myth and story, within the struggle between good evil, vampires are evil, so who else would be the good. God, of course and God’s representatives in most of the movies would be Christians because they were made for a mainly Christian audience. The riff on this is that anyone with faith in a good deity could presumably turn a vampire with a symbol of their faith. So the Jews and Hindus and Muslims would not be without protection. Although the Muslim would be tricky, I guess it might be a crescent but since Islam is strict about idolatry I don’t know if that is really a religious symbol. Anyway, it is the faith that turns the vampire not the symbol itself. The symbol is the focus.