The supermarket began to not carry certain products which were available elsewhere. Whether bad planning, unreliable distributors, various items were not there.
A customer would tell the purchasing manager, and expect that the items would be available the next week.
If a customer wanted the item, they went across the street, often finding other items they wanted.
Soon enough instead of spending X at the supermarket they would spend 1/2 X going across the street to spend the other half.
Some went and never came back.
After all, they came to buy A,B,C, D and the supermarket only had C. So why bother? Go where A,B,C, and D are available.