I work in a local company here and I dealt with many others in HK for some years. What I can said is there are 2 main causes of the staying back late issues:
1) many companies here are understaff, bosses want to give a good run of the money they paid and they expect 1 staff to handle 1.5 to 2 staff's work load. If you just capable to complete your own person work then they will regards you as under performance and will lay you off for other who can work like nobody's busisness.
2) the cultural here measure the value of the staff by quantity but not quality.In most cases the management regards those who work longer are those who contribute more. They dont want workers to "THINK" and they just want their worker to "DO" .
I was planned to use my personal times on weekends to study and recently I found that the management was not happy about it because I cant stay back and help other department on Saturdays. Amazingly, my company will expect their staff(from any department) to stay and work 3 days 3 nites in the office when the peak season come, you dont stay? lay you off~!