Trubisky had no chance running it on that 4th and 1. Montgomery missed his block on Smith, partly because Smith got a jump on the rollout. And the LB51 Barnes read the play before the snap and ran straight for the flat...
The Packers were jumping these rollouts early all game. They knew the Bears needed to get Trubisky out of the pocket. Nagy tried to adjust and throw the Packers defense off by starting to put Trubisky in shotgun and rolling him out that way, but the Packers still went for the sidelines.
Like it or not, Nagy is going to have to start calling some drop back pocket passes and Trubisky needs to convert some of them to keep defenses honest.