Very hard.
Saudi, Kuwait, UAE, etc. have oil income for their own subset of a “native” population. These are really small countries - or the population/livable area is small, the rest is useless wasteland. They can be more or less wealthy if they don’t have to spread it around to all the billion + believers.
Okay, okay I get the stats. My bigger point is that these dopes can be made to go home, even after settling for a couple of hundred years. All it takes is a little imagination (I feel a Lennon song coming on...)