Maximum workhours tend to be mandated by the chinese government, and obviously they have decided that x hours spread over y days is what they are happy with. From what I've seen there myself, most of the workers are scrambling to do as much work as possible - everything they are legally allowed.
Most do not see factory work as a long-term career - some do, progressing to line managers then project managers or R&D engineers, but that's the exception rather than the rule. Most of them are there for a few years, work really hard, make a (relative) pile, send plenty back to their parents then move on to something else. They're away from their families, their friends also work at the same place, so you can see how this makes sense to a kid fresh out of school.
I mean, the UK opted out of the EU working hours directive because it'd stop people being able to work as long as they wanted and whilst the sub 40 hour workweek sounds like a great idea for work-life balance, there are plenty of people who would hate it (like me).
Don't assume that people are being forced to work. It's a good job, especially compared to the alternatives, which is why they're never short of applicants...