Earlier quoted context omitted.
Have you tried coordinating entire teams to work on a shared codebase? Honestly, I have never been in an organization so large that this became a necessity (if you solve tens of different problems, that would require almost thousands of developers). But coordinating single developers without an API is hard enough already, I can only assume for teams its nearly impossible.
Define “codebase”? You can have multiple services, user facing apps or modules inside a single repository, but if there are no boundaries coordination will be difficult of course.
At least, that's what I understand from his comment.