I think B2N2 only tells part of the story. The lift force produced by a wing at critical angle of attack, at a given airspeed, is the same irrespective of the aircraft mass. But at a lower mass the Z acceleration produced will be higher (F=M*A, so reduced M means higher A).
So the bending moment at the wing will not change with mass (disregarding BM offset by fuel in the wings), but other parts of the airframe may have been designed to the G limit - maybe engine bearers, seat mounts etc.
So a lower weight would mean its possible to apply a higher load to those components at a given airspeed.