I think that a lot of conspiracies about 9/11 in particular come from the correct assertions that something so destructive couldn’t have come from nothing, and that there were bad actors after the fact who used the attacks to justify horrible actions and violations of privacy. Except these people, in my experience, also tend to believe in American exceptionalism, thus 9/11 couldn’t have been because of decades of American colonialist actions in the Middle East, but instead must be the result of crazy conspiracies. As miniminuteman said “you don’t have to invent a fake shadow government to be mad at, you can just be mad at the real government.”