Because the pixel count is not important beyond 12 MP. The size of the sensor and the quality of the imaging algorithms has far more influence on the quality of the final image. Unless you have been commissioned by an advertising agency to shoot 6' x 4' life sized posters, 12 MP is more than enough pixels.
If your images are used primarily for on line viewing, all you need is 3 MP.
There is no point having 23MP when the sensor size is tiny as is the case with smart phone cameras. Noise levels, color and dynamic range are compromised considerably. Besides smart phone cameras have tiny, cheap lenses which are generally the weakest link.
I shoot with the OMD EM1 and print A2 size images for exhibitions and the images are all razor sharp with no pixelation whatsoever. Large sensors with low pixel counts produce the best images with the least amount of noise and the best dynamic range.