Young people who live at home with their parents sometimes work late because they don't want to go home to their parents.
Alot of other people work late because they want to get noticed for promotions etc.
Some of it's self-inflicted. The first company I worked for in Singapore, the 'suits' as they are called (glorified sales people) would take requests from clients and commit at 6pm to deliverying the fixes by morning, then requesting the developers stay and do the work while they go home.
So there are definitely, 100% scenarios where it's not the company itself directly demanding employees to doing insane hours. But it does happen, China requires non-overtime hours to be capped at 36 hours. People are often not compensated for any extra hours they do.