The argument I’m familiar with goes as follows: Stores choose all their goods, bazaars provide stalls for merchants. People don’t like when one tries to masquerade as the other, or, be both.
Costco, being a store, can choose foods or goods that have been rebranded or independently sourced and no one really cares — they are still fully autonomous. They have always taken ownership of the product, so a change in supply seems to be completely within the store’s wheelhouse.
On the other hand, Amazon is a bazaar. Merchants line up, trying to get you to purchase from their stall using various tactics. Merchants get unhappy when they see that the bazaar’s guard uses their ledger to inform the head of the bazaar which merchants he could kick out. Not literally kick out, but be put in a worse position so that the bazaar’s own products are now the first ones people see.
This conflict of interest is in direct opposition of the merchants and may be in opposition of the consumers.
I personally really like Amazon Basics, as it tends to remove the brand cost. However, there’s a reason brands became popular in the first place — and the Amazon Basic brand is not one I associate with “quality”. I think the best part of the Amazon Basic brand is that it establishes a minimum bar of quality that Amazon generally needs. I know if so want the cheapest I go to them, otherwise I do my research or rely on brand reputation like I did before.
This is becoming more of the case with Whole Foods, which I’ve started to avoid. They were a quality store and that quality (seems to) have gone down. The issue with the Whole Foods purchase is that there are lower quality grocery stores already, so I’d be interested in how they’re doing with that market.