In the model you provided the probe is measuring at the end of a floating inertia. There is nothing acting on it to apply torque at that point. However, on the other size you have a motor accelerating that inertia and you will have a torque between the motor and the inertia.

If you probe between the motor and the floating inertia (I_1) say on the connection line. You will see a toque value that is non-zero.

(See attached image)