The reality is those graves and artifacts were being hunted and sacked for thousands of years for all kinds of purposes (mostly steal whatever they could, to melt the gold and sell the gems) as soon they stopped being actively guarded or cared for, or their religious value diminished along with the religion that they were made for.

More than that, surrounding people kept on repurposing materials from the temples to build other structures.

Every new empire that took over their land would plunder whatever value they could find to fund their army and enrich themselves.

This long term view of history of artifacts of old empires as something to be preserved at all costs, let alone in their country of origin is rather new - hell, the idea of a nation state is rather new.

Where are the ancient museums that were preserving artifacts of older civilisations?

Now, should they be given back close to their place of origin and historical context? My modern sensibilities say absolutely.

But I can hardly call the people that took them for the sake of inflating their social standing and preserving them in the process of displaying them in their collections special kind of assholes than anyone that came before them that wanted only to melt them down for cash - it was an improvement if only because were not as desperate as the people before them.