Why wasn't Mariota allowed to Play the last game

Just curious after seeing him come in when Carr was hurt. I thought he did well and that we would see him again the following week. He seemed to spark the team and he sure as hell is a lot more fun to watch. Carr seems like Grudens field general and is able to execute plays when given time. I think he has a better arm than Mariota but not as mobil with his feet. Watching Mariota scramble was fun and he seemed like he could be even better with more playing time.. If he had played and done well last game his value would of increased. A lot more teams would of been convinced. Why didn't Chucky let him start.

Given Chuckys contract it wouldn't of made a difference if we ended up 8 and 8 or 7 and 9 for the year. So why wasn't Mariota allowed to play ?