I have wondered the same thing.
Auburn fans in general are mystified by anyone's ability to doubt this guy.
Preseason last year, the experts predicted he would be a lower tier SEC QB. Brantley was going to be the talk of the SEC. I thought "Really? This guy is clearly a monster. This guy won the Juco National Championship seemingly with ease. Why assume he's going to fail at Auburn?" A couple of weeks into last year's season, any time anyone bet against Auburn, I'd think "Really?" "What makes you think that? Dude does what it takes to win, every single time" People saying he would probably be an NFL bust. "Really? What makes you want to bet against him this time?"
I guess I sort of get that. I saw the highlights in juco and said to myself (and others) "no way he can do those same things in the SEC. No way. He could just as easily turn out to be Brent Schaffer as he could Tebow."
What changed it for me was seeing him live and in person. Standing on the field and watching him toy with people. Like an enormous, well proportioned tiger pawing at a mouse. Jamarcus Russell was 6-whatever, 2-whatever, too. But when I looked at him he was all disproportionate. He had an enormous ass and big thick legs. Cam looked like somebody had taken a Ken doll and brought it to life. Perfectly proportioned and simply enormous. And he was just goofing around. Playing.
If you've never stood beside him and watched how scary good he really is, how little of his monstrous talent he's truly tapped -- and Jackson hasn't, Bradshaw hasn't, etc. -- I guess you just can't fathom it.