Part of the utility of Pantone is not just the color spec but the physical samples they produce that are the actual specifications and standards. They make color swatches and cards so that you can see for sure what everyone else will (try) to produce when you say "make this accent piece Pantone 13459 with a matte finish and this bit over here Pantone 9329 with a glossy finish." The utility isn't 100% just in the standard but also in producing those physical instantiations so designers and artists can KNOW what color they're actually specifying and can see it in different lights not just on a screen that might not fully replicate the color.

Making all those samples is tougher to do with an open standard, you'd need some certification body/process for a company to make for people to use to satisfy a similar niche as Pantone.

Pantone is an ink the public domain standard would be cmyk.

If you get five printers and ask them all to print C:11,Y:22,M:33,K:44 you get five different colours as each will have to mix their cmyk inks to get that colour.

Pantone is a spot colour that means you can buy a pot of ink thats Pantone 123 there is no mixing so the colour is always the same. If you want to print on glossy paper thats going to change the look of the colour so Pantone also do inks for each surface you want to print on, they also do dyes for plastics and clothes etc.

Edit: The difference between the five printers would be insignificant but if you are a designer or want your logo to look exactly the same on stand ups, pamphlet, business cards etc you would use a spot colour.

Because somebody hasn't done all the work. Why would they?

As an individual crafter/designer I could see myself developing specifications for a small number of colors I use in a project. Doing 1000s of colors would be a huge project that would need some way to pay for it.