google: understeer happens when the front tires have less traction during a cornering situation than the rear tires, thus causing the front end of the vehicle to have less mechanical grip and become unable to follow the trajectory in the corner.
If the tire had zero camber, the inside edge of the contact patch would begin to lift off of the ground, thereby reducing the area of the contact patch. By applying negative camber, this effect is reduced, thereby maximizing the contact patch area.
more neg camber on front = maximizing the contact patch area during a corner
grip better = steer better