Publix seems fairly well-stocked, but Wal-Mart often has multi-day gaps.
I think it has to do with cash flow. If enough cash flows to the manufacturer, enough product flows from the manufacturer.
When getting the ingredients together for a batch of chili at our very large “go to” grocery store, I could not find a bottle of ground cumin on the shelf. There were three brands there, and all three had seed cumin, but not one bottle of the ground stuff. I did find what I was looking for at Walmart, of all places.