Should we really be surprised that people don't want to be tracked everywhere they go? Isn't my location also a matter of privacy? I wonder where you buy one of these jammers.
I'm not so sure about others. If you're driving a truck for a shipping company, I suspect it's their right to know where their equipment is.
Agreeing to have such a device installed and then installing a jammer doesn't strike me as logical.
[EDIT] The only thing I can think of is that the GPS is always recording, but only examined in the event of an accident. The driver can claim the unit was defective and not his fault, so there's no proof he was driving 90 in a 60 zone.
The other option is that insurance companies and regulators want the GPS trackers installed, but the companies don't care as long as the deliveries get made.
There are limits on how many hours a driver is allowed to work, for safety reasons.
They could probably put a stop to this by making jammer detectors and inspecting for them at weigh stations and then checking the logs on the GPS for anomalies. If the cops have a jammer detector, they can start pulling people over for having them.
If a few people lose their CDL, they should fall out of favor. These aren't very easy to hide, given that they have to broadcast to work. And if this pushes them to invent some other way to tamper with their GPS monitors, so much the better: it wouldn't cause nearly as much harm as these.