I think it's two things really.
They like to just pound the hell out of the ball with Herron anyway. He's getting 25+ carries every game usually, and Hyde is the 3rd string. There's not many carries to be had.
And yeah, you know he's in the doghouse right now for the Twitter thing. It was pretty annoying to see them run Hall right up the gut three times near the goal-line (even though he did get in). Why not put Hyde in in that situation. I would give Herron 20+ carries a game since he's their best RB by far, use Hall with returns, in the slot and on screens and what not (though I'm not sure Bollman knows what a screen is), and Hyde as the goal-line/short yardage back. Keeps everyone fresh, but no... you're going to see Herron get it 30+ a game, Hall around 7-10, and Hyde won't see the field much more this year IMO.
Like Brewster said to Hyde, Herron's only got a few more games. Be patient, and you're more than likely going to be the man in 2012.