Part of it, I think, is that genre fiction simply has more tools available. That lets an author do their thing a lot easier, and in the hands of a master, is how you get masterworks. (I decided to check The Left Hand of Darkness off my list last week. Its introduction hits intellectually heavier than the last three books I've read put together. The introduction. And it's about five pages long.)

Of course, 90% of genre fiction is crap. (Bare minimum, I'll not argue with anyone who wants to argue for more.) But we know that. There's enough of it that I can find something interesting to read. I can't say the same for the last 20 years of literary, non-genre works. (I'll take pointers, though.)