My favorite theory from that whole debacle is that those guys actually went to the Las Vegas Sphere, which is apparently a giant green screen now (its not)

That's the problem. Believing in a flat earth isn't just some weird quirk, like believing that gluten is bad for you or the number 4 is bad luck because in Chinese it sounds like the word for death. You can have beliefs like that and still maintain friendships with people who don't share them. It's such an illogical belief that people who express it are always mocked, and it's also such a big "conspiracy" that believers have trouble not talking about it. That means believers tend to form a community to support each-other and defend against these insults. It's basically an especially stupid religious community or a cult.

Giving up on your belief that the earth is flat means losing your whole community. There's no real way to be a sphere-earther in the flat earther community. Some of the people "lose faith" but don't admit it to the others in the community because they don't want to be ostracized.

I would guess that the people who manage to leave the community are the ones who have friends and family that are willing to forgive and forget and welcome them back after they leave the cult. That also means that the ones who have lost their friends and family due to their wacky beliefs are never going to drop those beliefs because they'll have nothing left.