A photo is a view of an item. Angle, lighting, environmental factors chosen by the person taking the photo. These are all choices by that person. Creative/artistic choices in of themselves and in addition to the work being photographed.
A scan intended for reproduction is different. It is a best effort reproduction of an existing item. A copy. The museum made no creative choices. When you do a scan like this the optimal result is the ability to 100% reproduce the item. Molecule by molecule if possible but the exterior is always feasibly easier.
I'd be interested to see where these laws head as the future proceeds. Copyright law is a mess but not as much of a mess as those for patents.