I have friends who work at the local museums, and it is hard for them to judge intent.
I think a long time ago someone shot some photos at the Natural History Museum here and tried to sell them, so they went to a no tripod rule, unless you asked and explained what you intended, for example I needed some for a class I teach and they were fine.
If I needed a really good shot without the glass in the way, the photographer for the museum gave me some slides. Tripods can also be a safety issue.
I think it is obvious when someone is trying to copy artwork, and when someone is trying to make an interesting photo, some others do not and people love to bitch about someone else breaking a rule, so it is simpler just to ban it all.
At the Musee d'Orsay, it is so well lit I cannot think of many places you would want to use a flash. It is such an interesting building it would be a shame to not be able to shoot there, I have free admission there so I like to go back and see if there is some angle, or view which is more interesting than the last visit.
Good views of the Seine from the decks as well.
When I was in Journalism, the issues were entirely different, better to blend in.
Regards, John