If you are active, you know even one week of physical inactivity will set you back. If you are grinding, you likely don't have time to keep up a regimen.
The people voluntarily working unpaid overtime aren't doing so because they are so love with their work. Yes, they may love their work, but that isn't the sole reason. They are going in because they are lonely. They may have taken a job in a new city and haven't made friends. Or their friends have gotten married and started families and don't have time for them anymore. They may also live far from their families.
So they dive into work because when you are lonely, work is a way to give your life meaning.
This is the real truth they don't want people to know or even to admit.