People are all different, so the reasons for them believing in conspiracies cover a broad range of factors. In general, though, people tend to believe in conspiracies because of helplessness.I found that belief in conspiracy theories is strongly linked to insecurity about employment, alienation, lack of interpersonal trust, and minority status ...
I think the reason why so many people loved conspiracy theories is that they fascinate themselves on alternate truths and the version that makes everything better. It is so much a fantasy to some that they crave and would very much want to be true because it gives credence to their alternate versions.