App Icon colors reflect human biology.
Since I was a film student I put a great deal of study into the science behind the art and the pattern you noticed in App Icons exists in just about all color media. It’s no coincidence that it quite closely matches the color sensitivity curves of the human eye.
I think you can get a good idea of how we work by looking at how our vision develops. Babies in the womb are first able to see light and dark. The first color a baby can see is red. Black, white, and red happen to be extremely striking to adults as well and they’re used for purposes that call for a striking appearance. Stop signs and lights, for example, are probably red because it is very important that we notice them and our neurology is extra sensitive to red so it’s a good color choice for directing our attention to avoid an accident.
The next color a baby sees is green and the last is blue. Following the above logic one might think that order also reflects which colors we favor, but I expect there’s another dynamic playing an important role in our color preferences. We like contrast.
Contrast isn’t so much a matter of taste as it is a logical necessity. Without contrast there is no meaning. Light only means light in the presence of darkness. Contrast gives us something to bite onto and appreciate. Red can mean something to a baby compared to the absence of red, but next to its opposite it means even more, it is even more striking. Again, when we aim to catch attention we take advantage of the human biology by using high contrast images to grab audiences.
The peak of our visual sensitivity in the red zone is just about the opposite of the peak in the blue zone which means that even if one had no green cones and was therefore blind to green, one could still have a very well fleshed out color vision between blue and red alone. In fact color monitors are much better at reproducing the range of blue and red colors to which humans are sensitive than they are at reproducing a full range of greens.
I’m guessing at why these human preferences exist, but I believe it makes sense given the data. We’re far from being the only ones to notice this stuff: