Big Idea Non Fiction Book Review - What's Driving the Reader Through a Book?

One of the obligatory scenes is at the very beginning of the book, you've got to tell people what you discovered. And a lot of times that ends up on the cover as well. What do you think is driving the reader through reading a big idea non fiction book? It reminds me of a conversation i had with the guy that runs bard press. He publishes like one book a year.