This was a perfect storm of motives and emotion combining to make rational decision-making almost impossible. RG3 took over the locker room midway through their season, rallied them into the playoffs and wanted in the worst way to write the storybook finish...a run through the playoffs and a Super Bowl ring. Then they jumped out 14-0 in front of those FedEx crazies and the adrenaline really kicked in. He wasn't coming out unless dragged off. Shanahan, having tasted that SB champagne, bought in. Bad decisions by both.
As I said, RG3 wasn't their best chance for winning with the bad wheel...Cousins with wins over Cleveland and Dallas (if Shanahan had wised up earlier) could have competed with that nasty Seattle defense. May not have won but RG3's knee would be much the better for it and the backup QB's value would probably have risen, either as trade bait or stability in case the injury cycle continues for #10.
Ask not for whom the Senti trolls...he trolls for thee!