They should have all the resources in the world to recruit people that have proven to write good documentation. If open-source projects run by volunteers can have excellent documentation (e.g. Vue), why can't Apple?
Better docs mean a better developer experience which means more people want to (and are able to) develop apps for iOS which increases the value of their platform. It looks like a no-brainer to me to invest some resources into this to improve the current state of affairs.
I must be missing something here...