Earlier this month, Tanita said at Finding Wonderland that real science fiction is getting harder to find in YA. That was her experience after serving on the fantasy and science fiction panel for the Cybils. I served on that panel four (?) years ago and found the same thing to be true at that time in both YA and middle grade.
This past year while I've been doing agent research, I've found that quite a few of them aren't looking for science fiction. They don't say why, and it isn't necessary for them to do so. I, however, will be happy to speculate.
1. Perhaps they are already representing authors with science fiction material to sell and feel there is only so much of the stuff they can find a home for. This would make sense. However, since we're not seeing much science fiction being published, it seems unlikely that they already have their plates full of scifi that they're placing.
2. Perhaps they don't believe they can sell science fiction, so it would be foolhardy to accept new authors with scifi books to market. This would also make sense.
3. Perhaps they just don't like the genre, and not everyone can sell things they don't like. This is certainly understandable. I can think of several types of books I'd hate to have to promote to absolutely anyone, forget about editors.
Whatever the reason, agents are among the literary gatekeepers who control what is published. If they aren't interested in a genre, how is it going to get out into the marketplace?
Of course, all it's going to take is for one unknown writer to do for science fiction what Harry Potter did for fantasy and Twilight did for vampire romances and we'll be swimming in the stuff.
NOTE: I am not really Tanita's best friend. I've just been mentioning her a lot lately. I will go on to someone else soon.