In August issue of Discover magazine, Bruno Maddox speculates on why science fiction has ceased to matter:

For one, it was around that time, the mid-1990s, that fiction—all
fiction—finally became obsolete as a delivery system for big ideas. Whatever the
cause—dwindling attention spans, underfunded schools, something to do with the
Internet—the fact is these days that if a Top Thinker wakes up one morning
aghast at man’s inhumanity to man, he’s probably going to dash off a 300-word
op-ed and e-mail it to The New York Times, or better still, just stick it up on
his blog, typos and all, not cancel his appointments for the next seven years so
he can bang out War and Peace in a shed. If one truly has something to say,
seems to be the consensus, then why not just come out and say it? If your goal
is to persuade and be believed about the truth of a particular point, then what
would possess you to choose to work in a genre whose very name, fiction,
explicitly warns the reader not to believe a word she reads?

It's an interesting essay, worth reading in its entirety.