Process color has a limited color gamut when compared to spot color. Why does process color have a limited range of color?. Explain it in detail.
Pantone spot (or solid) colours are mixed to a formula from a base range of 11 inks. These are: yellow, warm red, rubine red, rhodamine red, pruple, violet, reflex blue, process blue, green, transparent white, and black. In addition to these there are also metallic and fluorescent inks in the Pantone solid colour range. All these colours are made from very pure pigments, some of which are chemical or mineral based.
Process colours are only made from a very limited range of 4 inks: cyan, magenta, yellow and black, and these are implemented in print by use of halftone screens for each colour separation, with a separate plate and print head or pass through the press, for each process colour. Metallics and fluorescent colours can't be reproduced using process colour.
A case in point: The Pantone colour Reflex Blue (a spot/solid colour) is a very vivid dark blue, and although you can get a fairly similar process colour, it just doesn't look the same as the solid ink. If you have access to some Pantone Color Guides, you can see the difference clearly. There's no point trying to show you by way of an image, as the difference can't really be seen using an RGB raster image on a computer screen. You have to see it in print to appreciate the difference.
TLDR: Because of different inks, and different printing methods.
The answer is pretty simple.
If you are going to have a process system that mixes colors. then the gamut of that system is going to be a n-gon of some kind. For normal CMYK process that means a triangle (though it, looks like a four corner one when plotted in XYZ. Because the XYZ space suddenly turns at red-magenta direction). Even if you'd had more colors youd still just have a polygon with the number of sides based on your colors.
Human, vision when plotted is not shaped like a triangle. More like an arc. Also the further to the corner you come the purer your color's spectra needs to be. So if you want to fill the entire human gamut you need infinite colors. (Or you print refraction gratings of some kind, such future tech is beginning to exist).
Now a spot color has no limitations, except chemistry and physics. Possibly also color suppliers logistic limitations. So in fact it is perfectly possible to have weird a spot colors. For example ones that glow, are metallic, transparent or ones that absorb nearly all light being darker than darkest monitors. The only limiting factor is your amount of money in your pocket. Given that spot colors have full freedom they can in fact be nearly anywhere in the visible range. Since, theres no limitation you have possibility to print stuff that wouldn't be possible in other methods.