Illegality /lack of documentation?
Aren’t there plenty of folks working in food service without proper immigration documentation? Maybe not restaurant owners but…
Still you need a population base although not as much as in the past
Quanjude had a branch in Rosemead in the 90s that was excellent but local Chinese /from different regions couldn’t see spending that kind of money for .18, duck dish banquets. They tried to cater to locals by adding some abalone and sea cucumber dishes to new banquet menus but to no avail.
Still 101 noodle did well without a huge Shandong beifang population