The reason being is that abroad you can get a part time job and make enough money to eat, have fun, and live. To many foreigners here it is not worth the money to get a part time job here. I'd almost rather be paid in peanuts (planters, salted)
Bars don't want to hire a Foreigner because why pay 20,000 rmb a month for someone that knows how to interact with people and smile when you can pay someone 1200 rmb from the village (although they have no personality, nor smile, nor shower). It doesn't add up.
BTW there are restrictions abroad for foreigners and part time jobs as well. Some can ONLY find jobs on campus.