My question was more about why the Solarize filter stops where it does and doesn't apply the final correction to get back to a 0-255 output range.
IMHO, the solarize filter in PS was created a long time ago, way before the actual "Preset Culture", where users expect to click on a button a get the "wow" result.
It is a tool that sets the basis for further editing of your liking, since the tones of the original image may require different tweaking of exposure, contrast, levels (all of them can be adjusted with a custom curve)
Have you ever tried solarization in a chemical darkroom? in my experience it required a lot of trial and error, it worked only with extreme contrast papers, and the flashing of the print had to be done during developing as mentioned by digitaldog, because if you did it before starting the development, you would get just a black sheet of paper. Too many variables that could go wrong and most of the time the results were crap.