I have been curious about this ever since the modding scene exploded after Oblivion.
In movies and games sci-fi tends to be more popular in general. Yes, there are mega sword&sorcery hits but as a genre sci-fi brings in much, much more money than sword&sorcery.
The exceptions being MMO and modding. But even MMO has changed as the derivative more popular MOBA mostly use sci-fi settings.
Modding remains the one area that sword&sorcery appears to be decidedly more popular.
I think your view of the market may be coloured by your own tastes. Franchises like LotR, The Hobbit, Harry Potter completely overshadow any sci-fi release, even The Matrix didn't come anywhere near those numbers. And then I'm not even counting the Pirates. Of course Star Wars might throw people off but really, don't call that sci-fi, it's pure fantasy/magic/swordplay which just happens to be set on an interstellar stage.
As a modder though, it's more about the tools and freedom. I'm a huge sci-fi fan when it comes to books/movies myself and have little affinity with fantasy, but there just doesn't seem to be a sci-fi game that allows modding on the scale and freedom of skyrim. Also, when it comes to gameplay, I think game makers have a tendency to push gun combat into the FPS realm, because that's where traditionally most shooters come from. Big FPS titles are typically PvP, where modding is generally known under the term 'cheating' and considered a bannable offense