It's a good question, and it's a very old one. Plato was an elitist who looked down on the "cave-dwelling" Greeks who couldn't rationally justify their beliefs. There was exoteric polytheism, which might have functioned like our soap operas, American Idols, and Kincaid paintings, and then there were the Mystery Religions and the dawning of philosophy and skepticism (proto-science).

It may have to do with the formation of large societies: the odds change as our nascent fallacies and primitive biases boil over and drown out our more enlightened inklings. There's also the Dunning-Kruger effect, which shows, as Yeats said, that "The best lack all conviction, while the worst are full of passionate intensity." The iron law of oligarchy has an impact, too: as power is centralized to manage the large group, the power elites justify their privileges in part by dumbing things down for the masses, even to the point of controlling the education and entertainment systems.

So there are likely supply and demand sides to this problem, as it were.