The rotation is because they stock the product for which they can negotiate the best discount.

But as you say the 20k SKUs premium stores stock aren’t a necessity. They drive up the costs for the store and the price for the buyer all so the buyer has the feeling they bought something different, when many brands are anyway the same product under different labels.

The premium store 3 minutes from my home stocks 30 types of mineral water. Aldi and Lidl stock maybe 3 of those 30. That’s what 99% of people buy anyway.