In your analogy you name two large brick-and-mortar retailers. Allow me to posit my own analogy: If Amazon is the Walmart of the web then who is the Costco? Who is the Target? There isn't any.

Retailers stick their neck out to put an item on the shelf because space is limited. The product is made. It's on the shelf. If it doesn't sell then someone loses money. If Equate brand sucks I can choose an alternative. If everything on the shelf sucks I can go to another store.