I'm not sure why you think that the Sky colors have a matte finish, all colors offered were a two part finish. First a color coat followed by a gloss clear coat. A matte finish is devoid of gloss or shine. What hot rodders would refer to as a suede finish. It's also been a popular finish for car wrap enthusiasts.
As far as the colors that GM/Saturn offered they choose to offer what was currently available from current models and called it a day. Plus Sky colors were tied to Solstice colors, and the Solstice was engineered to hit a price point of under $20,000. So again, GM didn't want to reinvent the wheel and choose colors that were already in production. I don't consider that cheap as much as I consider that smart.
Also, it has to be remember that upon the introduction of the Kappa program GM was (and the car market in general) imploding and needed government assistance in order to survive (including Ford https://www.factcheck.org/2011/09/fo...n-on-bailouts/
). So when I look back at that timeframe I'm not as concerned about the shortcomings of the Kappa as much as I'm glad that GM offered it at all.
While it may have been possible for the ultra wealthy to buy custom colors from ultra premium car companies for decades, it hasn't been that long for more mainstream car companies to begin offering optional colors for certain models at an additional cost. For the most part offering a few custom colors and marketing them as special editions is a way for a company to make extra profit at a minimum expense. It makes them (insert car company name here) look more exclusive, and makes the customer feel that their car is more special than the thousands of identical cars rolling off the assembly line.
For example, Volkswagen is suppose to start offering what is called Spectrum colors program in 2019 for the Golf R (for an an additional cost), but no one was offering this type of program for mainstream cars back in 2006.
Granted that it would have been cool if GM had offered a wider variety of colors, but the great thing about being a car enthusiasts is having the ability to modify your car to your hearts content. Don't like the color, have a custom paint job slapped on it, hate all the interior plastic, take it to a custom upholstery shop and have every piece covered in whatever hide or fabric you can think of. The sky's the limit (at a cost) when it comes to modifying your car to look like what you wished it would have looked like from the factory.