They’re brought together not necessarily by a strong belief that the Earth is flat (though most in the community strongly believe it, or at least pretend to) but because they were bullied as kids, socially awkward, had a hard time making and keeping friends, etc. From this angle I absolutely see how strong a connection these people might have to others in this community and why it would be hard to say “screw you only friends that I’ve ever had, your theories don’t make scientific sense”. They might lose the only friends they ever had.
This somewhat reminds me of the current state of politics. Why counter even a single belief, value, etc. that your echochamber has when they’re probably friends of yours and you know it could change your relationship for the worse (even though I think it’s ridiculous that questioning a political opinion with a well thought out, logically crafted counter opinion could ruin a relationship).