is similar to a car. Most of the brake bias is in the front. You almost never use a rear brake(or much pressure) on a motorcycle.
When the weight shifts to the front to much pressure in the rear would cause the rear to lock up and slide.
Even in low stiff race cars, rear brakes do not play a huge role in stopping or slowing the car. Pics I took of cars entering turns at night confirm a glowing front rotor, not rear.