That's not a great comparison, because of the way house brands are marketed -- basically store brands are marketed to the left of the name brand and cost a few margin points less. One of the reasons for store brands to exist is to incentivize manufacturers to buy the other product supermarkets sell -- premium shelf space.
Amazon is a big catalog, and they play all sorts of games with how and why they prioritize listings.
Amazon is a big catalog, and they play all sorts of games with how and why they prioritize listings.