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 ...
Well in essence, people believe conspiracy theories to explain things they do not understand. Also it give them another side or perspective, no matter how far fetched it may be. Sometimes, people believe in conspiracy theory mainly because people who explain to them are very convincing (con man-ish levels). It also involves factors where too many possibilities are involved