Costco has 1 store brand, Kirkland, that they are open about and in fact push it as a equal/better brand.
Amazon on the other hand has the Amazon Basics as an economy brand but also have these numerous hidden brands.
Costco also uses the same strategy to comeup with products. I used to see GT Kombucha and now costco has their own line of Kombucha as well. This is similar to Amazon where you observe the products at someones cost and make it inhouse if its viable. Another fact with Costco the costs being low is the businesses that sell at costco can only have as much as 20% of their total revenue from Costco -- which is like paying only for the variable cost as the rest 80% of revenue would absorb that fixed costs in supply chain. This is a huge bonus.