They have this quasi-religious cult vibe that makes them like this:

1. Sacred texts that give answers to everything.
2. Saints and prophets. I mean - they mostly identify themselves by someone else’s name - e.g. stalinists, trotskyists, maoists etc.
3. Aggression to outsiders. Building a good sect requires that, it’s how you keep folks inside - just make them hate the outside.

That’s not a scientific conclusion on my part, rather vibe-based one, and some conspiracy theory communities can also be described in that way. Which also leads to next conclusion - they’re kept in by a sense of community, and since that community is built around fringe and often cringe ideas - it only leads to doubling down on ideas that seem stupid or dangerous or simply not thought through to any sensible person.