Hard science fiction is growing less popular than fantasy because (A) science stopped telling people what they wanted to hear, (B) science started being seen as the cause of problems rather than the solution, (C) as science advanced, it started to eliminate more possibilities than it created, and (D) science has advanced beyond the ability of most sincle people to comprehend or stay on top of. Science stopped being a friend and started being an enemy so people have retreated from it into the more friendly world of fantasy, where anything is still possible and, at the wave of an author's pen, things can work exactly the way we'd like them to.
Of course Spider Robinson should complain. From what I've seen, he's a social liberal and they currendly exceed just about any other group in their hostility towards science and spending on things like space travel. All those feminists reading fantasy novels about unicorns and warrior women are not Republicans.
I seem to recall a thread about a year or two ago where Spider eviscerated the environmental movement. He may be liberal but you wouldn't have gotten it from that column he wrote.