On why some SF/F crosses over to mainstream readers, and why some doesn't.

At the Clarion Foundation:

He said that SF and fantasy writers grow up in the tradition of the genre and expect to be read by SF and fantasy readers. These readers bring a different set of expectations to what they read, compared to what normal people expect.

SF/fantasy fans expect to work harder. We know that certain passages have to be read with focused attention because they provide crucial information about the world.