What I have read, a major problem is getting enough people to pass the drug test.
According to trucking companies I deal with out west, passing a drug test is one of the major problems in hiring drivers. You want to make sure the person driving your $150K tractor, $50-80K trailer and the material on/in the trailer is not a screw up. Plus the liability IF they get into an accident.
Oh, I understand why they want clean drivers; I’m just surprised there isn’t a glut of them as people fall out of other fields but still have to earn a living.