As you'd imagine, there's a whole branch of psychology devoted to group dynamics and I find it fascinating.
From thousands of years ago and even up to present times, an individual's survival depended on being part of a group. Its not only the individual that chooses the group. The group chooses the individual.
There's a phrase, 'those like us'. Which is why candidates are advised to research dress, organisational histories, the social conventions and even speaking patterns of their target companies. To put into the mind of the interviewer that s/he isn't an outsider, but 'one of us'.
How individuals make meaning of everything around them is another huge branch of psychology and the preeminent research group of our times, was led by a Harvard professor called Kegan. His books are very readable and aimed at an audience wider than just academics.
Very generally, I think that the flat earth guy (I haven't watched the vid yet) is making meaning of earth and science now, using our part of the brain which was formed when we were nomadic tribes in Africa. At that time, pre science, what really mattered was the 'givens' that were handed down through generations. What we call superstitions. What not so long ago were regarded as fact. Like witches and the Salem Witch Trials.
As science and social science advances, I'm guessing that the majority of us are playing catch up. Although in some places the majority believe what their tribe tells them, over the impartial and independently established facts.
Like MAGA and the stolen election meme. This example, of many, illustrates why this branch of psychology is so important right now.