In the twentieth century, modernism and postmodernism took over, and their practitioners disdained beauty as bourgeois, saccharine, lightweight. Art was deliberately made incomprehensible or ugly or shocking... on the assumption that our predilections... were reversible social constructions. This also led to an exaggeration of the dynamic of social status that has always been part of the arts. The elite arts used to be aligned with the economic and political aristocracy. They involved displays of sumptuosity and the flaunting of rare and precious skills that only the idle rich could cultivate. But now that any schmo could afford a Mozart CD or go to a free museum, artists had to figure out new ways to differentiate themselves from the rabble. So art became baffling and uninterpretable—unless you had some acquaintance with arcane theory.
Steven Pinker, "A Biological Understanding of Human Nature" The New Humanists ed. John Brockman (2003).