I think what you call "development productivity" shows exactly the cancer that makes the Java ecosystem a spaguetti of jars (whith some of them being dead projects) instead of a lasagna where you see libraries use only other libraries from the layer "below".

But not, it is the obsession to turn everything into agnostic "engines" and meta-somethings, where everything is abstracted to the extreme with little value. At the end, Maven implementation using XML, plugins, dependency injection and having a build dependency chain of 100 packages did not prevent them from being kind of stuck in version 3 and slowly abandoned for another tool (gradle), leaving behind the only important value: conventions and the repository concept.

I can build/bootstrap ant and ivy just fine. And I can build almost every package using it by just telling them, don't go to the network, but use the one I already built myself with little effort.

If you ask why maven had to be packaged, mostly because it had to be patched with ugly hacks.