The problem with postmodernism is that it kills everything in its wake. Once you have been postmodern, there is nowhere left to go. In fact, everything you do after postmodernism, no matter how radically different it might be, can be seen as a reaction or a response to postmodernism. So design eats itself.
Autocannibalism was always what postmodernism was about. It was design consuming its own history and regurgitating it as a new, tongue-in- cheek avant garde. The fragments of classicism, the pieces of constructivism, the nods to vernacular and ad hoc traditions: postmodernism was an all-you-can-eat buffet of motifs and signs.
But it was one that was almost immediately subsumed by the consumer society it drew from. Easily caricatured as stick-on pediments and pyramids, the postmodernism that flowered in the late 1970s and 1980s became the language of the commercial developer, the mass manufacturer, the theme park, the casino and the homeware store.