You talk as if we develop code by chiseling it out in stone. We write it in text files, usually with IDEs. No one needs to learn the new libraries the newbie

You talk as if we develop code by chiseling it out in stone. We write it in text files, usually with IDEs. No one needs to learn the new libraries the newbie made, they can talk to the newbie, point out what the library already gives (and where to look in future) and write to well known interfaces. Any project should have time allocated for "tech debt" and that's where this sort of thing gets addressed.