It’s not just John Deere tractors that are being modified, but, JD is the one who is aggressively denying on warranty claims for tampered firmware. (Cat actively encourages some hacking on their products, but, their support guys won’t talk about the part of the firmware that is their geofencing.)
Part of the issue is compliance and equipment diversion – JD and Cat have to abide by federal laws that say that their equipment cannot be purchased or operated in trade restricted companies. In order to ensure that with the government, they have to have both internal controls (within the org) and controls on the equipment to ensure that they won’t work (think geofencing, only at a per-country level). Companies can get big fines for this – even if equipment was purchased by a third party who isn’t in an restricted country and they are the ones who move the equipment to the restricted country.
Nice backround info!