I know a lot of Korean and Chinese school kids who cram study until late and night and that is just normal. I suspect 996 isn't that weird to many young Chinese developers because that is what they've done their whole lives. 9pm is probably an earlier end than when they were doing homework.

Even in the US now children are getting more and more homework and stressed out about getting into the most prestigious universities. If that is normal when growing up, spending all your time in the office is just more of the same, except you get paid more than everyone else so society loves you too.