I saw the link ... and wouldn't waste my money since my cars don't have trackers (three are 1971 models that barely have an electric system). What I meant was that I could understand why people would want one of these devices.
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.
[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.
Agreeing to have such a device installed and then installing a jammer doesn't strike me as logical.