I wonder why apps and sites, both through the means of an OS, don’t use a contrast slider from -1=darkest..+1=lightest range, and also brightness and saturation

I wonder why apps and sites, both through the means of an OS, don’t use a contrast slider from -1=darkest..+1=lightest range, and also brightness and saturation, so that everyone could set a mode that is subjectively best for them. Because there’s no mode that is best for everyone due to how eyes work for different people and ages. Even CRT TVs had these settings, but not modern smart-phones, which know not only every pixel’s value, but even semantics. Also per-app per-site adjustments would be nice, in case some designer decides to force his preference through your color settings.