The fact so many people seem to hold on to absurd beliefs is something that has always troubled me. But, when you think about it, what’s the biological motivation for rationality? Sure, having an accurate understanding of the world around you will help with your survival, but as a social species surely social cohesion is more important? Thus, if other people in your tribe believe weird shit, your reproductive fitness would increase by adopting those views yourself. The existence and persistence of every religion on Earth seems to support this.
So, believing arbitrary shit because other people believe it too is actually the norm, not the exception. Scientific thinking requires one to overcome these innate limitations of the mind and call BS on your own (socially motivated) instincts. That requires a good deal of self-discipline and meta-cognition.
Where CTs get interesting is where the proponent actually harms their social standing by holding them. Part of that could be due to escalating commitment to an existing idea, part could be to strengthen a sense of identity to some subculture. Part of it could be narcissism. I guess plenty of other pathological thought patterns exist (such as addiction) so it probably shouldn’t be a surprise some instincts start misbehaving and feed themselves in a vicious, self-destructive cycle.
So, in a way, conspiratorial thinking is just a form of mental masturbation where one satisfies their desire for answers by making up their own.