Before the 1900s, some methods of mechanical reproduction did exist. These methods could be used to mechanically reproduce the written word and very specific forms of visual media. But one factor governed the creation of reproducible works: the work had to be made in a format that permitted reproduction. Put another way, the author of a work must have designed their work for reproduction, implicitly or explicitly consenting to it.
For example, a Japanese wood block carver chooses to make a wood block rather than draw directly on the page; this deliberate choice creates the means of mechanical reproduction. Even when this is done, the choice to do so often comes at prohibitive cost, and while the cost of reproduction is reduced, it remains nontrivial.
But for the rest of art and artists, exclusivity was not just implied, it was an expected standard. There is only one Mona Lisa. It was made in so-and-so year by so-and-so. Around this grew a nearly occult tradition of reverence for the individual, as expressed through their work - their true work, the one in front of you, unique and inviolable.
Through the 1900s artists were reckoning with the creation of film, and later, digital media. I won't rehash all these arguments. Suffice it to say that one main challenge was to the ethos of art itself. If the work is infinitely reproducible, then where has the artist gone? Today, anyone who wants to see the Mona Lisa has already done so. The original is a mere novelty, except to certain very rare specialists. This has only grown more true with digital media, as the ease of reproduction and fidelity have both increased dramatically.
Among a certain type of art culture enthusiast, or maybe dogmatist, there remains a belief that art has lost something material as a result of its reproducibility. And it is undeniably a reasonable belief that if people are provided the requisite data, they will, eventually, reproduce the artwork to a satisfactory degree.
To many of these people, call them any jeers you want, sculpture remains one of the last bastions where the occult value surrounding the artist, who made the work, has not been diminished, because no one has yet figured out how to mechanically reproduce a sculpture to a high degree of fidelity.
Certain museums hold this as a guiding principle, because it is their interpretation of what "art" is supposed to culturally mean. A 3D scan of a sculpture destroys that final bastion of sanctity against the oncoming tide of reproducible devaluation.
Now, I don't believe this argument is a good one. Frankly I think it's a bit Pollyanna, but I have to acknowledge I set it up so I could be strawmanning it a bit. But the reason we're not likely to hear it here is because, despite (what I suspect to be) its central importance to the Rodin, it is not, at its core, a legitimate legal argument.