because the hallmark style of postmodernism is appropriation. we all are locked into our time. even (dare i say it?) YOU, paul gardner, is a hopeless copycat when it comes to creativity. we can't think in new ways at this point. we live in a classic decadent culture.
note that the root word of 'decadent' is decay. we're on the downslide. the best a decadent culture can do is appropriate. it's all we can manage.
even psychadelia was a decadent style appropriating earlier ideas and styles. doesn't this look like surrealism? no accident.
try to imagine what the world looked like back in these days. for instance, think of that buddy holly poster - the boxing style one that recently popped up here. now imagine walking down the street in a world where posters all looked like that. then - WHAM! this suddenly whaps you between the eyes. it must have been such a mindblower to trip across this by accident.