https://www.abc.net.au/listen/programs/stuff-the-british-sto...
Things like:
- The current government in power may not allow the artifacts to be returned to the original people, but will accept them and place them in the national museum. In many of these cases; the original people actually oppose the "return" for now, and are waiting for the political situation to change.
- The current government actively blocks the return of artifacts as it would be victory for their opponents
- In some cases, the artifact would have been wholly unremarkable except for the fact it was taken by the British; that is it has a lot more significance as a "Thing the British Stole" and would have been lost to time otherwise
- Many artifacts require very intricate preservation activities that the receiving country isn't equipped for
- If the artifact involves human remains, there are all kinds of laws preventing the movement/transfer/relocation of human remains in both countries
In general I think returning them is a good thing, but more often than not there's an enormous legal/moral/ethical quagmire surrounding them
Edit: No judgement intended either way on this particular instance. I just wanted to provide a good resource if others are interested in learning more about the general situation.