it's a statement of fact, so we can just leave it at that. but the explanation as I understand it and I'm not a lawyer, is that scan or a facsimile is a mechanism of reproduction, and the act of reproduction doesn't give you copyright. work, derivative work, original work, demonstration of originality have all precise definitions, but in laymen terms which is also my understanding, your derivative work has to be creative and original in its own right to have a copyright.
So, if you scan it but add some clever upscaling mechanism, dynamic color curves, hyperspectral data, texture capture detailing the 3D surface, and use all that through some perceptual integration to give you a better reproduction than just a mechanical scan, you might be entitled to not have your case thrown out of court immediately.
Presumably, because it isn’t transformative enough to constitute a derivative work. Otherwise, making a copy of free works would allow one to put those works back under copyright.
Why not? It's derivative but it's still work.