The idea is to deliver small chunks of insight that is just counter-intuitive enough to be novel, but not so counter-intuitive that we can't take it at face value. It's a market that's developed in response to the fact that nerds are addicted to feeling like they're just a little bit smarter than everyone else.
I think the same rush we get from learning something counter-intuitive and novel is the same reason that many of us have read pg's essays - particularly the early ones.
Edit: It occurs to me that this comment could be seen as an example of what it describes...