You are saying a significant number of trucks are on the roads, but you are only comparing it to unit sales for *each* model of car.
Total up the unit sales of all the cars sold in this country, versus the units sales of light trucks. Then you will find trucks are indeed a fairly low percentage (*low* being in the eye of the beholder) of the overall unit sales in the U.S.
Allow me to spell it out. Say you have 10,000 light truck sales (arbitrary numbers) and the next vehicle is a car which only has 8,000 unit sales, but the next is another car, which has 7,000 unit sales and so on and so forth.
If it went:
10,000 trucks
8,000 car
7,000 car
6,000 car
5,000 car
4,000 car
3,000 car
2,000 car
1,000 car
9,00 car
Let's stop there. 10,000 truck sales versus 33,900 car sales. Get it? Just because a truck is number one in unit sales, does not make it a significant portion of all vehicle sales in this country.