Petrified Truth (via Outside the Beltway) offers a simpler explanation.
Outside of specific genres, such as children's literature, science fiction, and mysteries, most "literary" works are now unreadable and therefore unread. The literary class -- elitist, self-referential, Leftist, and often focused only on the most degenerate aspects of human nature -- has clearly outsmarted itself.
Worse, much of that stuff is sleep-inducing. It is no accident that the term "yawn" frequently turns up here.