Especially when the whole "gay" thing in Leviticus and elsewhere was aimed at temple prostitutes and worship practises of then competing religions. The "sin" was worshiping another diety, not the sex. But that's been lost throughout the centuries. So many people have been taught the lie that they all believe it's truth now.
And then there's the hipocrisy of anti-gay Xtians not follwoing rest of Leviticus while keeping the gay stuff active just because it fits their prejudices...