Have you ever looked at the historical demographics?
The area is nearly solely Muslim mostly thanks to the Muslim's history of being utter assholes to local non-Muslims, slowly degrading their numbers through murder, forced conversion and emigration to avoid the last 2. Part of the last one includes Jews, though Christians should get even more of the Arab land. There is no reason why the "forced conversion" segment should carry the sole ownership of the land.
I don't consider that a legitimate way to gain a proper right to a property.
There are no "other Celts" who got kicked out of Celt lands by France and the other Celt heavy states, those are their states now. If there was a nation of few million of Celts like that and they wanted a piece of France, we would be living in alternate history, and there is a chance they would get a piece of it.
And Americans gave Indians reserves anyway. Its not like anyone is kicking out Arabs from all the land west of Arabian Peninsula, even if Israel kicked out all the Arabs, Arabs would still have 99% of the land they conquered, as in they would still be making out like bandits from the affair.