Chinese school/university bosses, recruiters and agents are on the ball. They know they can offer low salaries and still get laowei to teach EFL in the most desirable cities. Qingdao, Dalian, Yantai, Xiamen, X'ian and Kunming are more examples of such cities where you can expect to receive at best very average pay despite the general relative prosperity there.
By contrast, backwaters offer relatively high salaries because it's hard to attract laowei to work there.
Of course, I'm speaking generally. There will always be exceptions!