A big part of the problem is that many museums really aren't set up to shoot well. Often times you can't back up far enough to get everything into the picture (or you have to back up too far and get something else in the way) unless you have the right lens. Also exhibits behind glass frequently have too much glare. And of course sometimes the exhibits are displayed in a way that is is difficult to get unobstructed shots. IIRC (its been a couple of decades), my problem at Les Invalides was that the flags were hung too close together to photograph individual ones. With CD technology it ought to be possible for museums to sell photos of their complete collections at relatively little cost to themselves.