I saw a blog post recently from literary agent Kristen Nelson, in which she mentioned that "urban fantasy" is hot, and "science fiction" is not. I have no doubt that this is true, or perceived as true by acquiring editors. But there's no reason this should be so, since science fiction and fantasy are actually the same thing.
Some small subset of science fiction is actually about science or technology. These stories focus on possible future problems that authors extrapolate from the possibilities of contemporary science. What are our responsibilities to a self-aware robot? What happens if some wealthy people are able to create super-children through genetic engineering? How will humanity relate to alien civilizations?
a wizard did it."
Similarly, there's no reason why southern vampire mysteries should be more popular than robot-noir, or whatever.
I am particularly fascinated by the categorization of Gary Shteyngart's Super Sad True Love Story as "science fiction." The book takes place in a vaguely hyperbolic near future, and I would call it a literary social satire. The only thing that's even close to a science fiction concept is the main character's company, called "post-human services," which promises immortality to the rich. But what they're peddling seems to be nothing more than plastic surgery, macrobiotic food and yoga. Oh, and the characters have slightly-better iPhones than the ones currently available.
One reason "urban fantasy" might be popular right now, though, is that "urban fantasy" is often actually structured more like a romance novel than a fantasy novel. Mean, rapey werewolves looking to be fixed by the love of a good woman are essentially the same as mean, rapey Fabio pirates and mean, rapey nineteenth-century British aristocrats.