It is also a certification issue. The brakes have to be good enough to stop an airplane at max takeoff weight from V1 ONE TIME. However, those same brakes have to stop an airplane at max landing weight MANY times. So, the brakes (and many other components) are built just large and heavy enough to do the required job (i.e., absorb all that energy without damage or undue wear), so more weight can go to passengers, cargo, and/or fuel.