Enthusiasts want small trucks. Americans don't want small trucks. They don't want a single-cab S10. They wouldn't even want a double cab S10. What they actually want is a minivan but they're too far into not-cool territory to be a consideration so they look to the mid/full-size SUV and/or truck segment. It is true that you can't really make a small truck in the US any more, and that automakers do like it that way, but it wouldn't change anything even if you changed the CAFE requirements.