Because it does not appear on the colour spectrum! The word pink was first used to describe colour in the 1600's to name the light red flowers in the dianthus family as 'pinks' a close relative of carnations.
However, light red is not pink as pink has a bit less green in the colour mix, pink is a fake or more commonly called a combined colour incorporating two different wavelengths of light from the colour spectrum that the receptor cones in our eyes perceive as one colour.
The ability of our eyes to do this is based upon the retina having three types of colour receptor cells, or cones. The first type, relatively distinct from the other two, is most responsive to light that we perceive as violet. Cones of this type are called short-wavelength cones, S cones. The other two types are closely related genetically and chemically. One of them called long-wavelength cones, L cones, is most sensitive to light we perceive as yellowish-green; the last type called middle-wavelength cones, M cones, is most sensitive to light perceived as green.
We See Colours the Same as Televisions and Computers
Put simply we perceive colour in the same way as televisions and computers as a mix of Red Green and Blue or what is commonly referred to as RGB, where the green replaces yellow as a primary colour. Regarding computers there is another format known as CMYK which is made up of cyan magenta yellow plus black which is used for printing as the use of black is more economical than mixing other colours.
Pink resonates near the base and at the higher heart chakra. Aspects of the base or root chakra are well known so I will not go into detail. What is less well known is the turquoise higher heart chakra which is located at the thymus between the heart and throat chakra which is about communication, therefore, turquoise is a bridging colour enabling communication with the heart and combining blue and green is sometimes referred to as the master healer.
We can see that combining turquoise higher heart issues together with the sexual aspects of the base chakra explains why pink is associated with sexual issues and not sex per see. It is to help resolve heart ache and maintain a sense of balance and to do this things can go up and as down to create an equilibrium. Going back to our RGB values while any combination of two different wavelengths can be used to add to the value of pink they need to be split to create colours that resonate at the respective higher heart and base chakra's.
