The licensing requirements for being a truck driver just aren't that onerous. It's way way harder to become a doctor, lawyer, hell, even hairdresser in many states.
A shortage of doctors is quite likely as many jurisdictions place price ceilings on doctor services.
In fact, where I live, it is quite illegal for a doctor to accept any amount of payment from a patient. We as a society believe that people, no matter how rich or poor, should have equal access to healthcare, so a doctor giving priority to a billionaire who can offer a handsome reward to get his common cold looked at over someone suffering something much worse is considered abhorrent. As such, we rely on a mixture of first-come, first-serve and needs-based priority instead of a price-based mechanism.
Never heard of any attempts to place similar restrictions on truckers, though. If you want to try and charge a billion dollars per mile, go nuts!
