Buildings are often protected as cultural heritage, even though they are private, the owner can't change them at whim, and preserving the looks is usually not enough. Isn't the situation similar with books or art?
AFAIK, with buildings these regulations (now) exists because they didn't in the past. People got really upset with other people just demolishing what they held dear, public outcry as a result and eventually regulations too. But in this situation the destruction is often driven by space being a scarce commodity (especially in cities).
I doubt that books often get destroyed to make way for new ones (barring a few criminal/extremist authoritarian regimes), so it might never have reached a point where enough people got upset about it and demand regulation.
But now I am curious though, if there are indeed regulations for these kind of works. If there are, that would essentially render my original opinion null and void.
Still, I would prefer it that way, rather than know that these works will end up in the hands of the financially powerful private hands. For I have little faith in that lot and their antics.
Plenty of countries have some level of regulation on this sort of thing.
After all, there's a long history of national cultural treasures being looted. Everything from the British Museum acquiring the Elgin Marbles under very sketchy circumstances to Hobby Lobby having a bunch of Egyptian and Iraqi artefacts seized.
Of course, it's debatable where such protections need to start. Only a defined list of items? Only items 200+ years old and worth $250,000+? More?