Migros is a co-operative, so its only way of spending profits are to increase remuneration to employees, return the money to the community (a large proportion of Swiss are "members") or re-invest into the business. It does not have shareholders like for-profit Red Hat, so paying a dividend is not an option for example.
If anybody has a pile of cash and has a busines plan for a co-operative Free Software company I'd certainly encourage it. But traditionally supermarkets were a good choice because they have so many tendrils connecting them with the community it's easy for their community to feel invested in the co-operative. Every company supplying the supermarket, and every consumer buying from it, can see the benefit of working together.