There’s a fascinating documentary, Behind the Curve. It talks about how, for a lot of these people, it began with the thrill of having some secret knowledge that others don’t, and then found they had a community and felt included for the first time in their lives (for some of them). That sense of community is really important to humans, so now, just like religion, there is more binding people to the movement than just the hidden knowledge.

(If I’m remembering correctly. I may be conflating it, it’s been a while since I watched it.)