Hood scoops became a necessity on muscle cars of the 1960's and 1970's as the monster V8 engines powering these vehicles needed cooler air. Pontiac found early on that making the hood scoops functional and funneling cooler air to the carburetor gave a dramatic boost in power. Things just kept getting bigger after that.
Cooling the engine is not the only function of a hood scoop. The engine bay area is about 50 degrees warmer than the ambient temperature, so funneling cooler air from outside to the carburetor increases power. The colder air is, the more density it has which means more oxygen per unit of volume. More oxygen available means you can oxidise more fuel per combustion cycle, creating more power.