Why can’t a full trailer truck be used as a towing vehicle?

A full trailer truck cannot be used as a towing vehicle because it lacks a front axle for steering, which is necessary for maneuvering. Full trailers are designed to be towed by a separate vehicle, and they rely on the towing vehicle for both power and control. The full trailer's design, where the trailer itself has no steering capability, means it cannot be used to pull other vehicles. It can only be towed by a vehicle that has the necessary steering and drive systems to safely navigate and maneuver.