Because the people who work at Migros probably have the right to an hour for lunch. They use this time to eat. This phenomenon can also be observed in other stores. There are even companies where, for example, nobody works between 12 and 1 pm (or even longer).

Counter question @Webütikofer: What does the majority of the Swiss population do every day between 12 and 1 pm? 🤦‍♀️