Tow Vehicle GARS vs GVWR

Because even if you managed to load the vehicle perfectly with the payload centered over both axles, the weight on the axles would shift the moment you turned the key and pulled out of the driveway. Every time you brake the vehicle's momentum will throw additional weight onto the front axle. That is why the nose dips when you brake hard. Every time you corner you are throwing additional weight onto the outside wheels. And if you are accelerating or climbing a steep incline you are shifting weight onto the rear axle.