Bakers needs a minimum amount of Volume that is greater than 1 sandwich shop. So a chain sandwich place might be able to Support a bakery but not just one.

The optimal quality model is for a sandwich place to contract out with a bakery for perfect bread but barring that a bakery can make great bread and ok fillings and still make decent sandwiches.

Think apple silicon at TSMC model for optimal quality results, intel model for good enough results.

The best sandwich shops will not make their own bread because it’s a lot easier to iterate without a bakery and 100 sandwiches shops can fail at relatively low cost for the one great one to shine. Capital costs on bakeries are much higher so you can’t just iterate in bulk. But you can get good enough at the bakery.