There is the obvious direct comparison with airline pilots. But it doesn't look like airline pilots became low-paid babysitters. This is still quite a respectable profession.
Because the pilots still have to be able to fly, which takes a lot of training, practice and certification. The skills called into play during a flying intervention are much more than the skills called into play by a driving intervention.
If a pilot walks, it's very expensive to replace him, because the pool of pilots are already trained and certified prior to a job app. An airline can't take anyone of the street and create a pilot. Or at least, they don't. Pilots are rare.
A trucking company can take anyone off the street and create a driver/monitor, in part because virtually everyone can already drive, even if they don't yet have a CDL. Drivers are not rare.
I don't buy into this logic. If you are able to intervene (i.e. suddenly take control of a large semi at its full kinetic energy in a life-critical situation), then you need skills of the same complexity as an existing truck driver. If you are not able to intervene in a tough situation, then the truck better be riding empty (with a procedure, for situations it can't resolve on its own, to stop and wait for support personnel to arrive on a car).
Yes, you do need those skills, but they are easier to put into someone off the street who has already spent years driving. People who have spent years flying are rare.
Training cycle for airline pilots is surprisingly short, less than a year if I'm not mistaken. It's just expensive because of all the gadgets involved.