Conspiracy theorists have a huge blindspot, an unchecked bias. They prefer for some irrational reason (usually to fit their narrative of the world, that also rests on biases) a less likely explanation (a worse model).
It is usually lack of certain empathy, overabundance of xenophobia or other kind of bias.
It's a very popular word these days, but what is "bias"? Some people assign different prior probabilities than others. Which of them are "biased"?
The people I've known who take an interest in conspiracy theories seem more open-minded and flexible in their beliefs than the general population. They may argue vehemently in favour of a particular theory now, but in six months' time they will probably have moved onto something else. But perhaps we're thinking of different groups of people. For me a typical "conspiracy theory" involves UFOs.
UFOs, lizard people, you know, like Hillary. And the Queen of England. And of course the Freemasons. Who are just happen to be the rich guys. The Youknowwhos, the Jews.
And so on. There's no big difference, or at least very short paths from one to the other. There and back again.
Everyone has biases. But some try to work around them, to maximize their own rationality.
The main problem is that people don't like to carry multiple models with them (after all, there's a very real cost to keeping multiple models updated, and evaluating them simultaneously and then checking which one is better over time according to some meta-goal), but that's the problem with these fat tail distributed events, like doomsday scenarios, conspiracy theories, "low probability + huge impact" happenings. Sometimes they do happen, but they are very rare and thus unlikely, and (!) in case of conspiracy theories it's very unlikely that people will notice it beforehand, because they are not derivable from first principles like an asteroid impact, or sentient runaway machine intelligence turning itself into an army of killing robots. So, our best bet against conspiracies should be systemic, built into our everyday lives, like anti-cartel regulations, whistleblowing protection, government and corporate accountability and transparency and so on.
It is usually lack of certain empathy, overabundance of xenophobia or other kind of bias.