Imagine what colors devs would choose if instead of defining white as "the brightest thing any given monitor can spit out" they would just specifiy some absolute value in e.g. Lumen per mm² and the screen tries to actually reach or maintain that value.

The issue with color on screens is a bit like the loudness wars in audio mixing: everybody tries to use the available bitspace to the max, because this made some sense in the days of 16 bit (or lower) audio. Nowadays much more dynamic delivery would be possible (with dynamic reduction as a user preference), yet there is no real, well designed system for such things in place.