Carter is always in the right place and never makes mental mistakes. Anae won't play other players (Burt being one) until he "trusts" them enough.
It's good and bad. Anae's players aren't usually out of position and don't make a ton of mental mistakes. On the other hand, Anae's system results in guys like Carter getting carries. Carter seems like a great guy and it's a great story, but he's just not a division 1 running back.