This lets the opposing defense play up close and shut down short passes and the run game. We were able to run against bad 3 front defenses anyway but against good defenses we can't do anything (see Utah and UCLA games).
Maybe Tanner isn't an all American yet but he opens up the field more with his deep threat. And more importantly he needs experience for next year. Why keep letting a senior make all these mistakes when we can let Tanner learn and grow for next year and possibly win more games now at the same time?