I gues the big Problem is that most users don't buy it but in fact get it supplied by their company.
Also many Truck devices are built in and not just stuck on the windscreen.
I know a company in Frankfurt that has over 50 Trucks in their park, but on none the driver has a chance to take the TT out or access the memory.
Without being registered as a company it is almost impossible to get the Truck stuff off TT and most small to single truck operations prefer cheaper alternatives or use AutoRoute with predefined routes for the drivers.