Basic reason why the PU's got huge is money. As in it costs almost as much to make a small PU as a much bigger one. But most people buy their vehicles by the pound/foot, so you can't charge as much for the little one as the big motha.
You see it with everything made in Japan. Accords the size of full boat Buick's, Civics bigger than an Accord 10 years ago. Just so the price can go up...Lots of chatter about whether American's will buy the high quality/cost small cars that the companies want to sell to get the fleet average high enough to meet the govt standards. AND make a lot of money.