You might think of this as the opposite of outsourcing, except these companies do outsource. However, they choose partners with relatively less negotiating power. Uber is an obvious example, but large companies like Apple, Amazon, and Walmart do the same at much larger scale; they can partner with large suppliers as long as they're relatively smaller.

This lets them control the user experience better and, not coincidentally, their own profit margins as well.

(I'm reminded of Gailbraith's theory of countervailing power, that large retailers arose because they had more buying power than consumers when negotiating with suppliers.)