I initially thought that, but the black door handles and rubstrip tie in the wheels and mirrors nicely, along with the front bumper and lower lip. That's it. Whereas the chrome roofrack, window vents, and factory tail/liftgate tie in some brightwork. If you wanted to paint the tails black, you'd have to chase the rest of the brightwork as well, and that would be an unnecessary hassle.
The older, good-condition brightwork gives it more of a retro vibe. Painting it black would cheapen the look, like you're covering up something wrong with the trim.