It's not that simple. A corollary is with cellphone firmware for the radio. They have to answer to the FCC. Updating the firmware will let you broadcast with more wattage, for example. FCC doesn't like that.

JD has to answer to the EPA. See Tier IV.

Automakers have to answer to the EPA too. That doesn't stop regular joes from changing their own oil in their garage and buying parts at Autozone. Most cars are not designed to make it impossible for car owners to do regular maintenance or simple repair jobs themselves.

Doing so would actually be illegal for the Automakers, who tried similar things in the early days of the Auto Industry and several laws and regulations were passed to protect consumers for Highway vehicles

It is highly unlikely this will work out very well for JD.

Yeah, it's called the Magnusson-Moss Warranty Act of 1975. It doesn't just apply to cars though, it applies to everything, including farm equipment.

That was one, but not the only Regulation passed as a result

Things like ODBII Regulations, which do only Apply to Highyway Vehicles, and all of the regulations that come out of the USDOT for Highway rated Vehicles.

As I understand, those contracts aren't legally binding, but they exist as evidence a company can point to in a trial to show that they tried to keep the user from doing X. An even more credible kind of evidence is actually making X technically difficult. Obviously they can't protect themselves against everything or they would go out of business (to use your example, they won't profit from selling stationary tractors). It's all risk management, and I'm not even saying I agree with their choices, only that their motives probably aren't as nefarious as Vice might want you to believe.