There's some history to laser availability, but right now, it's because you can make all those readily available colors from a light emitting diode. LED's are the same way where the only available yellows use phosphorescence to convert blue to yellow, which you can't do for a laser, and doesn't work all that well comparatively. If someone invents a yellow diode, they will get very, very rich because it is something the biomedical field needs as well as for displays and lighting.