The reason they can't do what he wants is that there's a legal requirement to keep the collection "complete", even though the remains were stolen.
It was stolen.
"Before Byrne could be buried, Hunter reportedly bribed one of his friends to secretly swap the corpse for dead weight and bring the body to him. Four years later Hunter put Byrne’s skeleton on display."
So a great, illegal, injustice was done and you're defending it because you didn't read the article.
What the museum should do is get a legal ruling that the remains were not legally Hunter's property so cannot be part of the collection and follow the wishes of the dead man AND what should have happened at the time.