I think you're missing the point. The bakery would have to sell "less-than-fancy" sandwiches, but the sandwich shop could sell sandwiches with bread just as good as the bakery would use.

The bakery has to become a inferior sandwich shop to make sandwiches. The sandwich shop doesn't have to become a bakery to bake just the types of bread that they need to wrap their sandwiches.

The bakery would be better off selling dough to the sandwich shop.