Nobody is stopped from working longer hours, but the expectation culturally is that you should probably be doing something else instead of working on Sunday.
And then, I go backpacking or bike-riding or something that tends to be demanding physically and relaxing mentally—I find it helps me keep a healthy balance. I know there are plenty of people that don't crave that reprieve though, and that's totally okay as well.
There's weekends where I'm working on a particularly interesting problem where I'll work through the weekend because I want to. The big difference is the extrinsic pressure is missing. Nobody has to.