> Then why scan them in the first place?

Just guessing but museums are always fund-raising through grants and looking for ways to expand their mission and justify larger budgets. Digital preservation through new 3D scanning technology seems like ideal grant-fodder.

At the time, the thought they could be compelled through FOI to provide the scan data to the masses who pay their salaries probably never occured to them. Instead of seeing the scans as an opportunity to share the museum's collection more widely (supposedly a core part of their educational mission), they see them as a threat to their defacto monopoly.