Supply and demand Because stupid rich people like to value themselves with things they buy and ART is so much more clever than the normal shit. If they buy expensive art then it makes them sophisticated and smart and better than everyone else. You can by taste after all. Best quote i've read in a long time"Freud said the goals of the artist are fame, money, and beautiful lovers."
That's reductive, though. When did rich people become stupid? When did art become clever? You'll note that there's still ridiculous demand for the Old Masters - it's not like the only art they're buying is crap. The issue is the only art being produced is crap - which is a wholly different problem. Here's a better quote: Art is the knack of making something from nothing and selling it. Frank Zappa