Another possible explanation is that the human eye is most sensitive to green, then red, then blue. Yellow, being lighter than either red or green, looks more like green because green looks lighter. With magenta, the difference is stronger because the eye’s blue-sensitive cones don’t register as brightness.
However, the colors on a computer monitor or TV aren’t ideal red, green, and blue. They’re not even close. The green resembles yellow because it is itself yellowish; ideal green is closer to the hue of a green traffic light. Monitors don’t use ideal green because mixing it with red would not produce a very saturated yellow.
In theory, all the colors available to the human eye can be made by stimulating the 3 types of cone cell in varying amounts, but in practice the spectral response curves overlap too much, so that there is no wavelength that stimulates only one type of cell. Cite.
In theory, we can surmise the ideal colors by measuring the invariant hues. Invariant hues are wavelengths that do not appear to change color when their brightness is increased. As you can see by the chart in the cite, red light stimulates both red and green cones, and blue light stimulates both green and blue cones. When a very bright red light is observed, it appears to change hue (becoming more yellowish) because red cones reach a ceiling of maximum stimulation, allowing green cones to catch up, so to speak. Therefore red is not an invariant hue.
There are 3 invariant hues, and they have been measured at 574, 507, and 476 nanometers wavelength (sorry, no cite as I got this out of a scientific article a couple years ago) which we perceive to be yellow, teal green, and azure blue, respectively. The yellow wavelength corresponds to where the red and green cones’ spectral response curves meet, so that they respond equally to that wavelength; when the light intensity increases they reach the “ceiling” simultaneously and the hue doesn’t change. The green hue corresponds to the wavelength where the red and blue cone response curves meet; this wavelength does not shift towards either bluish or yellowish when intensity increases. The blue invariant hue, however, corresponds to where the green and blue cone curves cross. Therefore the true primary color “blue” is not really blue. It is more of a deep indigo/purple.
True red, green, and blue are not the same as the colors displayed by individual phosphors on your monitor, and true yellow, magenta, and cyan do not resemble one primary color more than the other.
It is a common misconception that red, yellow, and blue are the primary colors. In the cases where these 3 colors are used successfully, the red is typically more of a magenta and the blue is universally a shade of cyan.