I would hazard a guess that the remains of a mummy still present interesting research opportunities, whereas the skin here is just skin, and there’s no real value in keeping it around other than the sensational. IIRC last time I was at the Museum of History in Ottawa they had noted that many of the indigenous artifacts on display are replicas - for many artifacts where they felt everything that they could learn had been learned, they have returned the originals to the people they were taken from. I feel this is a similar story.