Contemporary dystopias tend to follow the following basic format:
In a world wracked with global warming, our foolishness has depleted the world's supply of (Tungsten). As a result (Everyone over fifty) (is hunted for food.)
80s dystopias tended to go:
Largely Japanese megacorporations rule everything, and everyone has to live in decrepit apartments while wearing stylish sunglasses. There's a plot-line about an artificial intelligence, which doesn't actually change anything.
70s tended towards :
There are so many people! People everywhere! We will all live in tiny dormitories, and have to eat (krill), even decent white people, who deserve better. Behold, in sorrow, the world's last (butterfly).
60s tended towards:
There was a nuclear war. Now there are mutants with (psychic powers), who are also ugly. What was once the mighty United States is now a bunch of horrible little countries. (Cheese) is used as currency, and nobody remembers mid-list authors of the 1960s.
50s tended towards:
(Skunks) become giant and mutant! They are unstoppable! Only a (heroic scientist), (plucky reporter) and (small town cop) can save us all!
30s & 40s tended towards:
(Capitalism) is becoming increasingly monstrous. It will crush the nascent hopes of (Communism), which wasn't actually that much better.
I'll freely admit that there aren't sharp borders here. It's been a while since I've seen a classic post-nuclear mutant dystopia, but to some degree, and for some reason, zombies are standing in for giant ants in contemporary creature apocalypse dystopias. Also, if I actively liked reading dystopias, I'd probably be able to make sharper distinctions between the 30s and 40s.
But my point is this—why don't I have a model for a 90s dystopia? I mean, there were dystopias written in the 90s—Snow Crash, or Gun With Occasional Music, and so on—but they don't seem to feel like their own thing, in the way that a 50s movie about a giant mantis is clearly a 50s monster movie, and would be even if you made it today.