I would agree that there are obviously ways in which Apple could participate more in many of the open-source projects they use, but I don't really buy your point - it's literally source code which is open!
The idea is for Apple to release the source for components that are included in macOS, and the license requires publication. There is no obligation (or, I would argue, expectation) to do anything more.
Well. Okay. What I really meant to say is that Open Source - to me at least - can really call itself Open Source if there is a collaborative effort to maintain the code, ideally through a version control mechanism.
For example, Android is not Open Source to me because the code is dropped after the fact.
The idea is for Apple to release the source for components that are included in macOS, and the license requires publication. There is no obligation (or, I would argue, expectation) to do anything more.