Look at the long wheel base, the further the wheels are separated, the smoother the ride, the first wide track Pontiac came out in 1959, and was an immediate hit with consumers, not only for the smooth ride, but the high speed stability as well.
The 1962 Pontiac Bonneville had such a great ride due to having separated wheels. This separation was towards the fenders making the car have a full size that was comfortable. It also had stability and increased speed.
I had a 63 Catalina. Blue 2 door coupe. Loved that car. The rear wheel drive is another factor for handling on dry roads. Some of the high end cars today like BMW, that are not all-wheel drive, are rear wheel drive for better handling. Heavy car. 12 mpg.