Why is that, I wonder?
Are we really that pessimistic? Do we truly look down the road and see nothing but desolation? Bleakness? I know that cultivating ennui in a teenager is like teaching a fish to swim (I deal with teenagers every day, and while they are by and large a cheerful bunch, it doesn't take much to send them down the dark road of emotional futility) but it's hard for me to imagine that there is nothing in our future but the perpetual destruction of the human spirit.
The current political climate in the United States might, at first glance, to be consistent with a sort of pre-dystopia. The rise of very troubling elements in the right-sided political party is nothing to ignore. Climate change looms as an issue that threatens the globe. International terrorism is a steady source of anxiety or worse. And on and on and on.
Science fiction, it seems to me, is an inherently optimistic genre--the above exceptions included. Orwell would not have written 1984 had he not thought there was still some hope for us if we only looked and listened to the threat of totalitarianism. Bradbury ended the world in 451, true--but it was a rebirth. And Huxley later said that there was a third option for John Savage in his novel: one he wished he had written. Even the bleakest dystopian novel gives us hope--hope that humanity will survive (usually represented by the protagonist) or at least hope that WE will survive and thrive if we can avoid the warning in the work.
Even the characters in zombie apocalypse stories like The Walking Dead show optimism by even existing at all. They continue to fight and strive, and that is indeed optimistic.
So anyway, that's how I see it. Optimism doesn't have to be rosy. It just has to keep humanity in the fight.
Be seeing you!