I would say it isn't used as much because of creature confort. To annoying for people that live in changing climates. You don't want to ram your air when it's snowing, when you're following someone down a dirt road, when it's below freezing, etc.
It's just alot easier the the car-makers to put ten more hp into the engine and not worry about all the hassel of making room for ram-air.
Anybody else to help figure this out?
