Earlier quoted context omitted.
Camera cannot capture subtle details that are visible only through naked eyes and a creative brain to process
The only thing a camera is not capturing is any 3D details and light reflectivity. Unless you are trying to create an absolute perfect replica, I’m not sure why you’d need that level of detail. As an artist you should be able to add that detail yourself.
Other reasons include gamut limitations, interactions with light (as you've noted already), and the point of the exercise is to capture minor details and attempt to understand the artist's original decision making processes. That can involve looking at the artwork under different lighting conditions, from different angles and so on.
Photos of course make good reference pieces, but snapping a photo or downloading a scan of a piece is going to leave many frustrating questions unanswered.
Despite the outcome the goal isn't to reproduce the piece. It's to emulate the process that led to the piece.