Perhaps most readers just don't like short fiction any more--this is certainly borne out by short fiction having declined even more outside sf than in sf. Subtheory: If you want a half-hour's worth of fiction, television fills that niche. On the other hand, tv and movies aren't good at novels.
Perhaps it's an evil publisher conspiracy--it's easier to make money selling series of novels than to do all that editorial work just to end up with a short story that has to be grouped with a bunch of other short stories. I don't believe this one: it's quite clear that a lot of people love long novels and long series of novels. (Blaming long sf on word processors is a failed theory for the same reason--word processors make long fiction possible but not inevitable.)
This would relate to the idea that the natural length for fiction is long, and once sf had enough pretige that publishers were willing to produce long sf novels, sf expanded to its normal length.
Perhaps all the good short story ideas have been used up, so writers are forced into longer forms. This one is hard to prove one way or the other, but when I read best of the year anthologies and still like only a few of the stories, it's a tempting theory.
My best guess is that the field has simply been unlucky--we just haven't happened to have excellent short story editors for the past few decades.
Anyway, I've come up with a way of testing the hypothesis that people simply don't want to read short stories any more and/or there are hardly any short stories worth writing.
Fan fiction offers an interesting test case--it's driven purely by desire and has no economic constraints. However, I haven't read much fan fiction, so I'm hoping some of you reading this have. Are there substantial numbers of short fanfics? Are many of them considered classics?
Here are some links about fanfic:
On fanfic getting closer to the id than commercial fiction does
On fanfiction as the free play of the imagination--it doesn't set out to be subversive or anything else in particular
My imagination automatically turns things on their heads, supplies more of what I liked, resolves what I feel needs to be resolved, addresses what my own sensibility misses in any text, and it does that spontaneously, without conscious effort.
And a couple of short stories:
"A Lot to Be Upset About" This is simply the funniest thing I've read in quite a while. I think it would even amuse people who haven't read Harry Potter books or don't like them. This story is by Cassie Claire, who's also the author of the famed Very Secret Diaries, a combination of scurrilous slash and well-thought out non-slash silliness about the LOTR movies. "Where is the horse and the rider? No, really, that was my favorite horse."
"Black Is the Color", a classic about what really happens in the fitting rooms of the clothes store that caters to villains.
I'd be interested in suggestions for classic short fanfic and/or short sf online--the fanfic doesn't have to be slash even though my three good examples happen to be.
Final random question: if homosexuality becomes completely socially acceptable, will slash be destroyed?