I'm a manager. Why bring this up? To watch for people working too much and potential burn out. If people are working excessively, that's not good for them or the company. I want to be able to rely on people. That means knowing how much they can do. This means if they are putting in extra hours now, I come to expect that level of output from them. This is not fair to them, and not fair for the company. I don't want them burning out. I don't want them feeling as if they have to work excessive hours.
This is also why I actively encourage taking time as needed and being flexible when it comes to taking time off to take care of things during the day. It's a non-issue. Finally, it's why I pay attention to taking vacations. I actively encourage it. Often people feel the pressure of deadlines which are always looming. Through my actions, they don't feel as if they can never take time off.
Yes, I can see how you might feel if someone is watching your work hours. But it's not a single thing. It's a continuous effort and comes from a relationship you develop with the people you manage.
When I ask people why they are still working at a certain time, they know why I'm asking. The net result has been really positive for my team.