The sci-fi genre has really become a death stamp in the last 10-15 years or so for sales. The irony is that public appetite for sci-fi stories is near insatiable-- people just have come to hate the label.
A lot of novels that previously would have been written to a sci-fi (and ARE sci-fi, make no mistake) are written so as to sneak into the "Young Adult Fiction" category, so as to have a reasonable commercial future.