Well, Sci-fi in its heyday extrapolated the future as a continuation of the very high rate of apparent technological development and standard of living seen between perhaps 1940 and 1970. Then came the cancellation of Apollo, the space shuttle and all it failed to be, the oil crisis, Harrisburg, Chernobyl, environmentalism coming into the foreground...
No one is going to write a bestseller about what NASA might do in 20-30 years because people know what ever is being planned will very likely be canned. Dystopias can be a way to show facets of human nature that aren't always apparent in our own relatively comfortable lives. At worst it'll be an ill thought out and failed analogy to real and perceived injustices in our own world (YES BLOMKAMP, I MEAN YOU).
Compare that to utopia, which just like the latter will tend to be very colored by the political ideals and world view of the author. What is one man's utopia, might some times be someone else's dystopia, but dystopias, being more universal, are rarely the utopias of others. They're simply more universal. There is also the risk that "everything always ends well" removes much of the conflict/drama that drives the plot.