Several of the sculptures the museum scanned were plaster casts, including La Porte de l'Enfer and Les Trois Ombres. Given the destruction and reproduction inherent in the way Rodin's studio and foundry partners were producing bronzes at the time, the plasters are the most accurate, highest quality versions of the works, and are the closest to the hand of the artist. The molds used for the production of bronzes would have been made (and remade after they wore out) from the plasters. Accurate scans of the plasters are, arguably, therefore of much higher archival and commercial value than any scan of a subsequent bronze cast would be.
Not only that, many of Rodin's works were scaled up or scaled down from the original, using a pantograph.[1] When you see a monumental scale Rodin bronze, you're looking at something that was traced from a smaller version.
[1] https://collection.sciencemuseumgroup.org.uk/objects/co47993...