According to whom? Popular culture is where many of the "classics" originated. And I do realize that this is not necessarily the case with "Modernist" art, but artistic expression before and after the "Modernist" period was often popular before it reached the status of canon. Some examples within the art forms are Chaucer, Shakespeare, Byron, Tennyson, Da Vinci, Michelangelo, etc. Thus, "popular culture" is more important than it may seem.