Because its not print. Only print nerds love CMYK.

It’s a valid question because colors from an emitting light source use RGB whereas reflective would make sense to use CMYK. As a practical example a 4 color CMYK eink display may look better than or at least equal to the 7 color display above.

The frustrating twist is that - under the hood - this screen is CMYK. There’s a magenta “ink”, which would fill out a huge gap in the colour gamut, that we can’t even use. The same applies to cyan. Both colours are fundamental to the display tech and yet poorly represented in the very boring 7-colour palette.