The discussion on this specific graph is fairly scientific and not about cultural color perception. I changed the wording to "hue" to be more clear. Magenta and purple absolutely do not exist on the electromagnetic spectrum as their own wavelengths. Every other hue of other colors we can perceive does.
"Primary" and "secondary" colors are not scientific terms, but cultural terms.
The evidence is right there in physical reality, a rainbow or a prism will not include magenta/purple, because the colors between red and blue are not part of the spectrum. It is an amazing thing that we can make up these shades in ur minds.
But I was wrong in my original comment, because the red-blue connection can also be done by making a color wheel, ie making a complete curve.