It's also incredibly common for mothers not to have sufficient supply regardless of formula use. This results in a negative spiral where the baby won't be fed enough, and the mother isn't able to sleep, resulting in even less supply. Formula allows the mother to sleep, and the baby to be properly fed, even when they mother wants to breast feed.

See, your problem here is you're assuming the mother is the only one feeding a child.

I deliberately said “new parent”.