Turn that around...
Why is it that people only implement the dystopian visions of science fiction writers?
Why is it that the most plausible (thus often most popular) future fiction is at least partially dystopian?
The answer is framed within the question, on purpose: "most plausible".
A related question might be: Why has Philip K. Dick's work been adapted to film more often than any other SF writer?
But, it strikes me that even in the darkest dystopia, one can always find a hiro protagonist.
Wouldn't it be nice if, just for once, somebody latched on to a positive sci-fi concept and made it real?
Tried that once, and we got the Apollo program -- then lost it. 35 years since the last footprints on the Moon...