In general, Arab states and Palestinian leadership argue that naturalizing refugees would undermine their right to return to their original homes. You can interpret this cynically: because many Arab states are not too friendly with Israel, having a massive class of refugees putting political pressure on them could be advantageous, and is probably one of the only ways to "defeat" Israel as a jewish state (because if all of those refugees had the right to live in Israel, jews might become a minority.) But it is true that removing refugee status without a just solution would erase Palestinian claims and rights under international law.
Seriously though, if you look back far enough, all land is stolen. I think it's more prudent to focus on the present day.
Why not?
While much smaller tragedies are used to justify forever war by Hamas against Israel.