Answer
The bar increases the person's moment of inertia and makes it harder for torques to make the person fall down.
Work Step by Step
The bar increases the moment of inertia, since mass is distributed farther away from the center. Since torque $\tau=I\alpha$. This means that $\alpha=\frac{\tau}{I}$. Therefore, as moment of inertia increases and torque remains the same, the angular acceleration is less and therefore it is harder to move the tightrope walker.
