So putting myself into an asshole NIMBY's shoes: I bet a lot of people don't want to admit that they would prefer not to rub shoulders with people who needed foodbanks. And that is likely a major reason why a store wouldn't do this.
Also you'd need to staff it and if the food is free, that's an expense. Also the store space could be used for other merchandise so you're paying for a bigger footprint and to light, heat, cool, and clean it. I've been to some food banks and rarely are they in nice modern buildings.
I agree that it should happen instead of food being wasted. Those are just the reasons it wouldn't happen in a commercial store. I think a better idea would be to strictly regulate what food is allowed to be thrown out vs mandatory donating with huge fines for intentional contamination or waste.