Counterpoint: YKK (look at your zipper) relies on absolutely no one else for its supply chain [0]. This could easily be seen as a waste by those who would say YKK should just source its metal from the foundry down the street. It's easy to do a quick thought experiment in your head to think about how feasible it might be for every company to vertically integrate the way YKK has. On the other hand, YKK can't get jerked around by greedy corporations looking to take advantage of their dependencies.
[0] https://ykknorthamerica.com/the-ykk-difference/vertical-inte...