I think you will find museums, as well as most institutions in the USA, are more conservative than in other countries because we have to beg door to door on an individual basis rather than facing the press (which can be brutal in the UK I am told) and the governmental bureaucracy as professionals do in those places where the preservation and transmission of culture is a function of the government. Not only do we have the press and a notoriously fickle government that is fragmented into local, state and national levels, but any civic organization or gang of nuts can make our lives hellish. We simply don't dare to take the chances. If they had hung an I. M. Pei pyramid on the front of the Smithsonian Castle building I am sure some reactionaries would have formed death-squads to hunt down the perpetraitors.