Hans Haacke

Q1. The Guggenheim decided not to show Haackes installation because it was too "political" and "alien to artistic purposes" but then why will museums show art pieces like Duchamp's Fountain which is a ready made and is nothing special? Isn't art supposed to be thought provoking? 

Q2. Rosalind Deutsche says that "great art" has "found shelter within the museum, where it can be united with other aesthetic objects defined as products of unique artistic subjects" (170). Haackes artwork, i believe, is quite unique; it challenges the position of the museum and raises political issues. So what makes an piece of art unique? Why isn't Haackes work considered "unique" or great?