I think I understand the problem, but I think "able to provide breast milk" seems very open to interpretation. Babies are disruptive even before you have to pump or feed every 4 hours. But if you stop even a few times the body will stop providing milk. If your schedule doesn't support that (or you screw up occasionally) it will have a big effect.

However, that really means that you're not willing (ex a few percent who would have had dead children) to do what would have been required a few hundred years ago. Formula for a majority is a convenience... and has been since we used wet nurses and cow's milk.