That’s it how the grocery trade off happens really though. I’m not familiar with the particular stores you mention, but this market is sliced up the same way here, I expect.
First off, the stores are not fungible. Secondly, most people are trading off a convenient option for a much more inconvenient option or two, not 30s more driving. So say a extra 1/2 hour to your trip, or more.
Why aren’t they fungible? Because they don’t carry the same products. There is an overlap of commodity products (cans of coke, big name cleaners etc.) There are product a more bargain store won’t carry at all, and then there are products that are superficially commodity (cheese, meats, dairy, produce) but really aren’t.
Of course marketing makes this all more complicated if you want to think of “rational shopping” but it’s still true that the mid and high cost stores know I would probably be happier to pay more for truly commodity products there, than make a separate trip for them. For the most part, for most people, that’s true - although cf CostCo and the like for specific counter examples based on less frequent trips to “stock up”
