The problem is that 99% of art, (be it literature, poetry, music or sculpture, etc.) is crap.
The vast majority of that crap almost nobody ever sees, in the world of books and music you have to get published to get attention that filters out something like 90% of the complete drek.
Not everybody is a creative genius, this is also true in technical fields, something like 90% of innovation is driven by 10% of the population. This is why our society has people we pay to critique art and tell us what is worth paying attention to. (And sometimes they are horribly, horribly wrong...)
The point is that SOME performance art is amazing.