Why do so few hatcheries sell Red Star hatching eggs?

"Red Stars" are hybrid birds; the rooster is one breed while the hen is another. Because of the genetics of the two breeds, the Red Star chicks are "sex linked," meaning that the color of their down when they hatch is linked to whether the bird is male or female. This means that males hatch out a different color from the females, so they are easy to tell apart. Generally you buy Red Star chicks when you want to be assured of getting all females---they aren't vent sexed like other chicks, so vent sexing errors won't occur. Ordering sex linked birds allows you to avoid vent sexing errors.

However, if you bought eggs that would hatch out Red Stars, you'd still get a "straight run" mix of males and females, so the bottom line is that there is not much attraction for buying eggs that will hatch Red Stars.

Plus, most people who hatch at home eventually want to breed their own, and since Red Stars are hybrids, they won't breed true. In other words, you can't breed a male Red Star to female Red Star and hatch baby Red Stars. What hatches would be a "mutt" kind of mixture---very nice birds to be sure!---but the second generation of birds would be different with that background.

That said, there are some designer hybrid breeds that are very attractive. Generally these will be birds that produce similar offspring... or birds that have blue or olive eggs... or birds that have other unusual qualities or come in unusual plumages.

There is nothing wrong with cross breeds, but in terms of interesting backyard pet chickens, Red Stars probably fall relatively low on the list. They're more like a sex-linked Rhode Island Red, designed for easy sexing and high production.