It's not a "learned" thing. Go can pull it off, because it's much younger, and doesn't have so much accumulated cruft. Eventually they will - and then they would either have to make the decision to break compatibility in some future major release - or become the next Java in a sense that there are parts of the language and the library that are warts upon warts, that no new code will ever use, and that confuse new developers, but which are needed for old code to run.