Museums think they own their artefacts, and they want to control who gets to "publish" them. Typically museums have a few archaeologists that they have close ties with who get the privilege of publishing stuff. If some random person comes along, god forbid from abroad, they will try everything to stop you from getting access to their collection.
They often don't even have time to publish their stuff, so many museums have unpublished objects in storage that noone knows about and they more or less keep secret because they want to decide who gets to publish them.
This fiefdom affects big and small museums alike.
One tactic that occasionally works is to get some important institution or some well connected professor to contact the director of the museum and sweet-talk to them to give you access.