They are public domain, but we need, as developers, to be able to build the libs.zip file.
The discrepancy I found between developers page and git repository is a clear example of issue we can run into (we could build/package the full software with different libs).
In fact I don't disagree to get a zip file (given it includes all licences text for all of them, I did not check them at all), given I can also get a doc to build it myself, with instructions/how-to
Maven is a solution, not the only one : A simple doc for those into full rebuild could be enough (or a download script with a correct build-libs.xml).
This is not a priority, however. Just to keep in mind.