what have i been up to?

In May I was in STL, visiting my family and friends. 
This past week in of June, I was in NYC visiting friends, visiting museums, eating good food, drinking lots of Hoegaarden and Guinness.
Between STL and NYC I went to the Van Gogh exhibit at the Seattle Art Museum.
Yesterday I got my Kayak out into Lake Sammamish.
I really like the new Modest Mouse CD.
I am reading The Collapse of the Third Republic, because I find that sort of thing interesting and the French Guy I eat lunch with sometimes said he failed history and had no idea what went on.

So my question is, why I can I not get prints of every piece of art work I come across?  Why do museum shops only have prints of the most famous paintings?  Is there some wierd copyright thing going on?  Is it not cost effective?