Indoctrination and ignorance, notice how a big chunk of its members are old people. Younger people are less interested, thankfully. Also, for some people, it is a social club.
I thought about that as well. I'm not religious and i don't know anyone who is, but i talked to some elderly people of whom i knew they are religious about it. And surprisingly, they pretty much gave up on it. One couple told me how ass their childhood was because they were scarred into believing in fire and brimstone when they don't behave. The other lady who was very Christian, said that she wished she didn't basically wasted all theis time with Christianity, even tho she liked the whole community aspect of it and the "tradition."
And like i said, religion isn't part of anyone's life that i know, especially in my age group. But for the last 2 years or so it started popping up on tinder that Christianity somehow is still going. Not strong or anything, but it went from nothing to seeing two or three jesus freaks a month or so.