Because you might end up with your life at risk like this guy
Vehicle Stability and Handling Demonstration
The tongue weight is the static force the trailer tongue exerts on the hitch/tow ball. Proper trailer tongue weight improves the vehicle and trailer towing experience by improving performance. Not enough tongue weight or force on the hitch/tow ball causes an increase in trailer sway from side to side, making it difficult to control. Conversely, too much tongue weight or force on the hitch/tow ball could overload the rear tires of the towing vehicle, pushing the rear end of the vehicle around. This could also negatively affect the vehicle handling. Performance is impaired as you might not be able to go around corners and curves properly, and your vehicle may not stop quickly enough when you press the brake pedal.
The Weigh Safe Drop Hitch effectively measures the tongue weight of your towing load, improving the vehicle tow load balance and performance.