Because the things you have in the fridge change. The opening and closing of the doors change. The actual equipment changes. Store hours change. Holidays happen. Sports games happen. Weather happens.

To be honest, a grocery store is one of the most dynamic systems I can think of.

Edit: A bang-bang thermostat is not an appropriate solution for a grocery store.

That's called a thermostat and doesn't require remote control. The frozen food needs to be at the correct temperature all the time, regardless of external factors.