Outside of teaching, it still has some of the best paid expat positions.

Also, many people (teachers included) have married Chinese women and have children. When you've set up a proper home, making the move elsewhere is not as easy as when you're a typically nomadic kind of worker. You've got to get visas for your spouse, arrange shipping, arrange schools for your kids,get yourself a new job there; save more money in advance than usual if that's going to be difficult etc. For some, exiting a country can take a while.