If you know french bureaucracy, it is very simple in the end. It is a public worker that is nominated as the head of the museum. The mindset is almost never to do their job well or benefit the common good. But to be important and showing your importance by abusing your power if necessary to show that you have some.

Somehow he thinks that the sculpture is his own as he is the custodian, and so that he has all rights. And pictures or 3d scans in the end belongs to him also, like if the virtual thing was a physical item locked in the museum.

If he is forced to release publicly the 3d scan, especially against his goodwill, it is like being striped of his power and authority so he couldn't allow that. It becomes a personal matter.

The only thing that could have worked is to befriend him or create a cultural organisation and have lobbied to him in the first place that he would learned a lot of reputation/marketing points by releasing it. Imagine a dedicated website and grand champagne event with the incompetent minister of culture where they push the button...