That's true for basically all store brands including Amazon Basics.
Kirkland usually is not a top of a brand category, except when they are putting out marketing to let you know how good their vodka is, but they are never competing at the bottom either.
The construction company my dad worked for was hired to redo the concrete flooring in the factory sockets were made. He told me how the sockets would come down the conveyor belt and then get pushed down different paths. At the end of the different paths, the sockets were stamped with Husky, Craftsman, etc. Different company names, same socket.
And how could they be? Costco makes their money off membership fees - Amazon is attempting to make their money on driving their competitors out of business through what can only be described as monopolistic practices. Costco isn't an open bazaar that tracks goods sold and enters markets where they see "vendors" being successful. They sell a small number of items at a fair price - and don't intentionally screw their suppliers.
I literally can’t think of a single Kirkland item that was used to run a name brand out of business. And they don’t do any “special placement” either.
Amazon on the other hand....