And what is the point of this scholarly thread? That car companies made different models from economy cars to high performance models?
People did not buy many hemi 'Cuda convertibles in 1970 for the same reason that not many people buy Hellcat Challengers or ZR-1 Camaros marked-up $20k over sticker today. They are an odd anomaly on the showroom floor that are fun to look at for a minute but almost no one actually wants to own, at least not if they have to pay for it. They are one-trick ponies that don't serve people's transportation needs.
And therefore become rare, collectible cars later.