I think it was more about the fact to save paint, the painters were instructed to only paint the tops of the engine compartment, or what you could see after the engine was installed.
I have 5 '75 cars, and they are all like this.
I agree with the paint in the engine ompartment ...NOT a lot and runs! They would pinch a buffalo nickel till it pooped in their hands. Cheap bastards!
Many of our old cars are restored to way better than they ever came fro the factory. After all thy were mere cars to drive wear out wreck!??