D&D "Religions" were done badly from the get go:
Others and even myself have gone on about it in other threads. But it all boils down to the fact that most RPG writers have no idea how to portray religions in their games in a meaningful fashion.
Religions in the majority of RPGs are so badly done that if actually taken at face value they would have the PC's act in an alien fashion to how actual people of faith would really act. So people instinctively bounce off of the inherent incongruence of D&D style "religions" as they are really just mostly setting flavor that give some PC's cool powers.
Yes, because largely they cannot write religions any better than the garbage that passes for D&D cosmology, take the path of least resistance, and just sideline the whole thing.
Which is probably the better solution for most.