Back then brakes were small and wheels diameters were small and tire diameters were large. Performance tires of the late sixties and into the seventies generally had 60 series aspect ratios. The ratio of tire height to section width. To make a whitewall or RWL tire requires andding 2 more layers of rubber to the sidewall. A thick layer or white and a thin layer of black. The top layer is then buffed off on the tips of the lettering or completely around the tire on a white wall. Since cars now all have disc brakes, the rotors need more clearance for air circulation to cool them. So wheel diameters have increased, where now 18" is the most common rim size and to keep the tire from getting too tall the sidewall had to shrink. Everything is now what was once called Low profile. There is not much market for 14 or 15 inch tires so slowly the tire manufacturers have discontinued them and sold their molds to smaller companies that can survive on low production, high unit cost tires. Just like the Wide whitewalls are usually seen on cars from the fifties, RWL tires are marketed for cars from the late sixties/early seventies. The tires are safe just made to fifty year old tire technology. "appearance over performance" Fuel injection used originally in aircraft and diesel engines crossed over to racing and high end performance applications. Fast forward and most people don't even know what a carburetor is. That is the same technology gap that there is between bias-ply tires and radial ply tires. Tires are a major part of the suspension system and required a complete overhaul of the rest of the suspension to complement the radial tires unique steering, braking characteristics . Rims had to be strengthened, shock absorbers revalved, suspension parts tolerances tightened, etc... tires are more than just the round things that support the car.