Might be more useful than our own speculations about "why do people believe X?"
Bounded rationality proffers the assumption that your typical sapient agent makes decisions on the basis of imperfect information. However, on this site we've been just as likely to deal with individuals who have perfectly good information, but are unable to accept it or choose to ignore it. This is why I myself have often answered the question of "why" by noting a spectrum of possibilities — ignorance, anxiety, gullibility, delusion, dishonesty, boredom, cruelty — with the caveat that all we can do ultimately is respond to arguments and claims, not psychoanalyze those who make them.
In terms of people who actually believe fantastic claims, I think this explanation by Michael Shermer is far more relevant to what we see and do around here, and it has the benefit of being targeted at a casual audience.
