As far as I'm aware, it's only confusing if you're poking around in the source tree, rather than using the built docs at docs.python.org (where the link to the legacy docs is now hidden away inside the distutils module docs).

The legacy docs remain in place to preserve existing deep links and because they're the only current documentation of various distutils details that are needed to *implement* tools like pip and setuptools.

In a more ideal world, we'd have a distutils expert with the time to go through the legacy docs, cull the outdated stuff, and lift the rest up into the distutils module documentation, but all the folks that might plausibly have the expertise to do that also have far more interesting things to do with their time :(