“Can you name a single movie made in the last 40 years that depicts a future that’s better than the present? I can get as far as one of the possible futures in Back to the Future II, and then I come up empty. … Somewhere between the assassination of John F. Kennedy  and the fall of the Berlin Wall , the future [anticipated by our fictions] turned ugly. It stayed ugly for decades.”
Possibly it has something to do with the eliding of ‘the teenager’ into political rebellion in the 60s and 70s, with dystopia offering a much freer rein to imagine one roaming free of one’s parents strictures and their ‘crumbly old’ society. Plus, the threat of nuclear war offered a real and ever-present chance of civilisation’s collapse.