I beleive the real reason why peoples' imaginations are retreating from science and space, and into fantasy is becuase, as already mentioned, the future does seem to be here. Science fiction seems to have lost it's mystery as generations of scientists have slowly reduced fantastic tales of black holes, into a bunch of numbers and statistics.
That isn't enough a reason though, for it doesn't explain what motivates people to move towards fantasy. I beleive the explanation for that lies in what we beleive the future and the past hold. Years ago the world thought of the future as endless possibilities, with technology drawing mankind closer together, and closer to their dreams. That differs wildly from what most believe today. I, for one, see the future as a place where technology rules, and people have been dehumanized by technological innovation; reduced to components in a machine. That is what drew me to fantasy.
In fantasy, the people are the heroes, rather than the technology. In a day and age where most people are slaves to a cubicle, people want to be able to retreat into a world where there is still mystery and where heroes still live. In a day and age where the closest thing we have to a hero is the guy two cubicles over who got us the 5 cent raise; people want something more.
I think that's why peoples' imaginations are retreating from science and space, and into fantasy.