Migrants move around to follow the work. (Think more like "Nomad") Immigrants resettle in new places.
I'm reading more about it, and probably these restaurants survive based on a combination of:
- Family run, keeping labor low (labor always number 1 cost)
- Central Asian and Muslim customers (much more than just Uzbeks)
- Setting up in low-rent locations like strip malls
So a few big nights a week can sustain the family business. I guess there's a way it adds up to a profitable business.