Consider that for a lot of shops and restaurants demand might be inelastic over the course of the week. If everyone in town is closed on Sunday and consumers don't have convenient access to other options it's likely that demand will simply shift to other days, thus being closed on Sunday would reduce operating costs without significantly affecting revenues.

This is arguably a big factor for both Chick-fil-a and liquor stores that are prevented state-wide from opening on Sundays (in the US)