In my experience, many people who should know better are afraid that if they return cultural artifacts they won't have any to show. The idea that people might cooperate or share with them simply doesn't occur. Which is wild, because many exhibits are not filled in this way.

"Africa is Not a Country" by Dipo Faloyin points out that 80% of African artifacts on display in museums are on display OUTSIDE of Africa

Like nobody needs to yell "finders-keepers" or aggressively shrug about the unknown provenance of a German-American immigrant history exhibit because they know where they got their stuff and they can stand by it.