Why have him run when you have a stable of talented running backs. I don’t want him getting hurt - live to play another down. That being said, oline needs to protect.
You have him run to keep the defense honest, without it the DE crashes down and takes the run away from the backside.
The QB is not accounted for by the defense, that allows them to flow to the ball carrier, watching the replay there were numerous times if Purdy kept the ball, he could have went right around the corner for yards.
Granted ISU has been unlucky with injuries on the QB's, but that is not a reason to give up running the ball by the QB.