Can't even imagine the amount of crap in their code-base. I bet that amount of commits is necessary to continuously correct the shitload of mistakes coming from their "Hacking" culture.
They deal with this with automated code review tools like their Infer static analysis tool (http://fbinfer.com) as well as abstracting away the Objective-C with React Native.
Yeah that might work for programming mistakes, but not sure it can help with bad design choices.