The trucking industry has gotten very savvy when it comes to insulating itself from liability stemming from trucking accidents.
These companies know that because of the sheer size of these vehicles, collisions cause severe injuries and major damage. They also recognize the principle of vicarious liability holds employers responsible for the negligent actions of employees, or vehicle owners for the negligent operation of those vehicles.
So the industry has become extremely fragmented. Most truck drivers are independent contractors. The rigs are owned separately from the trailer and often the load being hauled is owned by yet another entity. Then there is usually an agency that arranges those connections.