I subscribe to Locus magazine to keep up with the news of the F&SF field. One of its many features is the annual February edition with its qualitative and quantitative summary of the previous year in publishing and how that relates to previous years. Among other interesting parts of this edition are the graphs of the numbers of books published in various categories.
One graph shows that the number of F&SF books has been very slowly increasing since the early 1980s. Then around 2000 they began to steadily rise, with a slight dip in new books in the last three years and a corresponding increase in reprints. The overall total stills trends upward, but suggests a shift of publishers from the more cost-intensive new books. That last might sound like bad news for new writers, but it does have the bright side of keeping pro writers bread-and-butter, their backlist, pulling in money and introducing new fans to them.
Another graph shows the relative numbers of fantasy and sci-fi books over the years. In the early 80s SF was clearly dominant, though not by much. All during the 90s they were even. Then in 2000 the number of fantasy books published began a steep increase. Today they account for almost twice as many as SF.
Looking at the two graphs it becomes clear that the number of SF books has remained essentially the same for the last twenty years. The rapid rise in fantasy in this decade is what accounted for the rapid increase in the number of F&SF books.
So why do you think fantasy is whipping SF butt so badly? Harry Potter? The popularity of urban fantasy and paranormal romances? Something else?
PS Here is the web site for Locus (in which I have no financial interest).