I feel sci-fi and fantasy are very underrated genres. They require a lot of creativity. Because in most cases you have to go out and create this whole new world, different in so many ways from reality. It's not easy sometimes.
I don't know why they're grouped together. They're very different. Sci-Fi usually involves space, aliens, or technology and the future. Fantasy on the other end involves different realms, realities instead of actual worlds (which would be more sci-fi). It tends to be magic, or creatures only told about in myths, rather than aliens.
Most of the time they're not given a fair chance. But when you write them, you know that going in. You write them simply for the love of writing them. You can't harp on reviews or read counts. If you do, you'll just drive yourself crazy. Or if you harp on them for everyone to see, it's almost like asking for pity reads LOL. You just can't do it, there's a readership for the genre but it's smaller and you gotta accept that from Day One.
Sometimes you can bring in more readers if in some way, the Boys are still the Backstreet Boys rather than having it be an AU. But that's not a guarantee. I haven't written sci-fi in awhile, but it used to be a majority of what I wrote. Sometimes I miss it, though I have future ideas I'll one day go back to. There's something to be said for creating that whole new world, it's so fun to write in it.