I can't tell if you're being sarcastic. Are you literally saying that art must remain geographically located at its origin forever? That seems insane.
The British museum paid for most of their artworks. Granted, probably not what they were worth, but certainly a price the sellers were willing to accept.
We might consider them "priceless" objects in a museum now, but that doesn't tell us anything about what they were worth at the time of acquisition. The "value" of an artwork is almost entirely a cultural construct, not something inherent in the object, and may vary drastically across both time and space.