Big companies with lots to lose will always use a waterfall process. Facebook can move fast and break things because there's little risk to them, but fintech, legal, military, and medical software will always require peer review and a waterfall process. When I was a mainframe programmer at IBM, it was the waterfall process that protected customers from untested code and, as a result, you don't hear much about giant hacks or thefts in things like bank accounts, Social Security checks, or industrial manufacturing. That's because the suppliers of those programs don't want to move fast and break things. They want to move slowly and be sure that software works, to the best of their ability, before shipping.