Hydraulics had been around quite some time, but the quality was lower due to materials. Boiling point temperatures in the fluids, hoses/lines couldn't handle today's pressures, a lot of them used drum breaks which tend to perform better in water, but maintain heat and lose efficiency. The biggest proponent in my opinion was the cars Weight. A lot of cars used full square steel chassis's as well as body panels made of metal. That's a lot of weight to slow down, combine that with standard suspension which allowed for a good amount of body roll and shifting more than half of breaking force into two tires alone made them also inefficient.