What premise is false? The WMF does provide database dumps that don't contain the relevant author information. They also provide database dumps that do contain the relevant information, but they call the dumps without the information "the archive most mirror sites will probably want". Thus they should (ethically, at least) make it clearer to reusers that more information is required if they believe this to be the case.
I stand corrected. Having now actually downloaded one of the dumps, I see it only contains the username of the most recent contributor to an article, not previous contributors. That's not good... shouldn't be too hard to fix, though - I'll take a look at the relevant code.