Originally I would have said it was because the world just doesn't have enough Depression Era Fords, Tri-5 Chevys, or '69 Camaro kits available yet and those are far more important to bring more mundain kits to market first...............
I agree with the Cheetah, however it should be possible to build the rest with some kit bashing and aftermarket parts and decals. I would rather see more truely rarely kitted subjects being newly kitted or reissued like the Cheetah, more modern workaday cars and trucks, as well as updating the tools of the few modern cars that do get kitted.