Most of these third world countries also have some artefacts on their soil as well. Do they need literally all of them, and you'd have to visit the globe to see international artefacts? The most famous ones, like the Rosetta Stone, only became famous from their usage by Western archeologists.

As for London being expensive, well visiting any foreign country is expensive by non-natives. At least in London you can get a large set of cultural exposure in a single visit.

> Most of the people whose cultures those items belong to cannot afford to go visit the museum.

There is no ancient Greek or Egyptian alive today, those cultures are long dead. What claim do modern inhabitants of those regions have over these artefacts?