Potentially to skirt driving time limits?

Many lorry drivers are paid by the trip. If they get stuck in traffic, they are losing money. They are also required to take regular breaks, to avoid fatigue. If they jammed the GPS, then the company can’t prove they didn’t take their break, and worked through, to make up time.

It also allows for disallowed detours. “Sorry boss, I was stuck in traffic for over an hour”. In fact they went for a pub lunch, on the clock.