Three words:
Human rights record.
there's usually a chinese teaching assistant who is fully fluent in English
"well why don't they teach them English then ???" I hear you cry
well it's because the chinese only deem to be learning "proper English" if they are taught by a white faced westerner
All these rich families (parvenus?) in Shanghai and Bejing want their kids to be taught by native English speakers. They don't care if they need to spend a fortune because rmb are like toilet papers to them.