Honestly I think a lot of it is tenuous evidence and so-called 'experts' with fancy titles that don't mean anything ("According to ancient alien theorists...") connecting the dots in combination with distrust towards governmental bodies to be forthcoming with the truth. And on some level maybe a lot of people just want the monotony of their lives to be broken up by the thrill of a conspiracy which would be a huge crux in all of human development. On an emotional fulfillment level it's not really something I fault people for, only when it gets to the point of ruling their reasoning skills.