Some rules "enforce themselfs". Unpaid overtime brings positive motivation for emplyers to broken. Paid overtime is negative motivations, and people are more likely to report it and sue due to lost money.
As I said, you start by creating a culture where rules are enforced, then work from there.
Sunday is free because it is 'overtime'. Workers are paid fixed pay per month. Suing for Sunday would not bring any extra money to worker.