I used to stuff shelves at a grocery chain ~20 years ago and one difference seldom mentioned is that grocery chains bought from the manufacturers. That meant that we as a grocery chain were responsible for the sale to consumer, we were not merely a marketplace for a bunch of different brands.
So, even if we had our own competing labels for some products, the manufacturers would never be left in the cold with unsold stock (if for example we chose to drop one brand or run a promotion for our own).
So, even if we had our own competing labels for some products, the manufacturers would never be left in the cold with unsold stock (if for example we chose to drop one brand or run a promotion for our own).