I'd say that those who leave will miss the short working hours and being
allowed to be out of school when they have no classes if they are teaching in the public
education sector. They'll also miss getting much higher salaries than Chinese colleagues
and living in better accommodation than new Chinese teachers, said accommodation being
at least rent-free. And they'll also miss the non-accountability of the teaching if they
were high school teachers teaching oral English with no end of term exams.

Bullshit! You are either a wumao or a very, very naïve foreigner.

Chinese staff do indeed earn a lower basic salary, but are legally allowed to work in second jobs or run businesses on a part-time basis. No visa violations to worry about. Then there's the grey income - Mercedes and Audis don't buy themselves, you know?

Many Chinese teachers that I've met already have an apartment of their own and will commute to work on a daily basis, many teachers will even sublet that apparently not so great apartment to students at the university! Yet more grey income that appears for them to be perfectly, socially acceptable to receive! That's before we even start talking about those Hongbaos!

Most foreign teachers are expected to hold not only end of term exams, but in many cases mid-term exams as well.
Some universities do observe teachers and although training centres may merely use a T.A as a spy, some (and sadly, still only some) actually have quite professional staff observing their teachers, not to mention class monitors who will at least snitch to the bosses if a teacher got a little bit too lazy.

Teaching at public universities is quite an easy job, but it doesn't mean that's better alternatives to consider elsewhere.

You are presumably teaching at public universities in China, but your reading skills aren't up to much. I wasn't talking about uni teaching! Yuncheng agents provide FTs mainly to high schools. There, FTs have much less work to do than Chinese teachers of English as a rule. I didn't mention that Chinese staff have to watchdog students 2 hours/evening for private study. We FTs don't do that. Fact is, you're naive, you know next to nothing about senior middle schools in China! My job is much easier than yours. As an oral English teacher teaching for Yuncheng agents, I can let my TA deal with classroom management in its entirety.And I need only prepare one 45-minute lesson/week with her help if I wish it. I've got the better job, not you! End of story.