My belief is that taking the time to write docs is kinda like an editing process of your thinking. You start to think hard about the reasons you've written an API and how it could be better. And there's a limit to how big you can think about something as a whole so you will naturally try to modularize and layer things. Not just adding things in an adhoc fashion.

I think they threw the towel when they realize the mess they've built. In contrast you have things like RHEL, FreeBSD, etc, where there's a drive to keep things small and neat just to be able to document them.