It's a rejection of the privileging of metaphysics of absence that has largely defined Western culture since Plato introduced his theory of Forms. The idea being that what is "real" or of "value" is not something outside of one's self or the experience that an agent must get to, but rather informed or constituted in the now.
Or to put it even another way: Being weird for the sake of being weird.
It's replacing them with entirely new barriers. For every actual piece of art in a modern/postmodern art gallery, you have about 50 people who are just collecting trash from the side of the freeway as some sort of ecological statement, or deconstructing their essence into a representative graph of wishes vs. deeds, or saying "fuck it I'll just rip off DuChamp."