In my old "blog" (of sorts) I have written extensively about conspiracy theories and believers in them, and the reasons why people believe in them.
One aspect of this is, I think, that believing in conspiracy theories is a form of pseudointellectualism. Especially people who have memorized hundreds and hundreds of arguments and can flood a discussion with them in a form of rapid-fire and shotgun argumentation, probably get a sense of being quite smart and "educated": They have the feeling that they are experts on the subject in question and possess a lot of factual knowledge about it, and thus can teach it to others and use all these "facts" to argue their position and win any debates.
In other words, they are pseudointellectuals. They feel that they have a lot of factual knowledge on the subject, and they might get a sense of intellectual superiority, even though in fact they are just deluded. They are often good at debating and arguing their position, but they do not realize that they are spouting nonsense. Of course this nonsense is wrapped in tons of seeming logic and apparent valid arguments, which superficially might sound plausible when you don't examine nor study them too profoundly, but it's still just nonsense.
The same is true not only of conspiracy theorists but also of creationists, ufologists and believers in the paranormal. (When we examine all these positions closely, there actually isn't much difference between them. They are all basically religious belief systems.)
I think that it's precisely this sense of intellectual superiority that makes at least some of these people so firm in their beliefs. They might not admit this even to themselves, but deep down this feeling of superiority makes them feel good, better and more "educated" than other people.
In fact, some pseudointellectuals use precisely their own sense of intellectual superiority to belittle their opponents.
Perhaps the most prominent example of this, a pseudointellectual on a completely different level of its own, is William Lane Craig. He feels superior for having an education on "philosophy" and has several times belittled his opponents for not having such an education and therefore not having the necessary "qualifications" to debate him on the same level.
This is just an outstanding level of douchebaggery. An incredible amount of smugness. And this even if philosophy were any kind of relevant field of science (which it isn't, which just makes his attitude even worse.)
I don't think it's easy to surpass this level of pseudointellectualism.