> then you visit the original country where it’s from and they themselves have nothing or very little left from that era.
You seem to generalize quite a lot in order to validate your view point that everything stolen should stay stolen.
Sometimes it's the entire opposite. It's not being shown anywhere, it's just hidden in a museum collection in the UK. In other cases it's exposed but with very little relevant information because it's not particularly relevant to the local culture or the colonizer is too ashamed of the real history of how this object got there that they fail to explain the true story of it.
Here's a great podcast that I hope will make you change your mind, lots of examples: https://www.cbc.ca/listen/cbc-podcasts/1030-stuff-the-britis...