Tesla for example lets you pay to access their diagnostic software, so why is John Deere the bad guy here?
Also, there's something special about tractors. Their owners (farmers) are both willing and capable of repairing tractors, in general, so John Deere is demonized for taking that ability away. Where as Tesla's owners are comfortable not changing their own oil, so "less" was taken away. (Yes, I know Tesla doesn't have engine oil, don't get hung up on that)
And yes. I am happy to expand that list to literally every other manufacturer you have in mind. They are all bad guys too. If manufacturers were altruistic good guys, they would need no regulation.
Regulation is the solution to this prisoner’s dilemma.
I can grab any data I want from the OBD port. The hardware was cheap, the software to use it is, again, free.
I'm not excited about this brave new world where you have to pay a subscription fee to plug a cable into a device you own and interact with it, and even less excited there are people here defending the idea.
The cheap OBD2 readers lack the vast majority of data and tools you would want to use for service as well.
There are aftermarket options but most manufacturers want you to subscribe to their service tools - often charged per monthly plus an additional a fee per VIN it touches. These cost in the hundreds to thousands. It can be pretty frustrating as a shadetree mechanic.
Theoretically, they are to be replaced at 120k miles (!!) but they won’t even tell you that in the owners manual.
Insane.
I work on a project related to it and was absolutely surprised at how the company gave instructions to the clients to help them fix their machines (stuff I wouldn't be able to do myself).
Having a non-working machine can mean big $$ lost everyday.
Here's how it's always worked for me:
1. A code comes up on the computer.
2. A. The problem is self evident. Or;
2. B. I search online and find the problem. Or;
2. C. I search online and find the diagnostics manual, which I use to find the problem. Then I have diagnostics manual pdf forever, and can use this in the future.
3. A. I search online and find the parts diagram. Or;
3. B. I search my dealers website and find the parts diagram.
4. I order the part.
5. I install the part.
Has something changed with newer equipment that prevents farmers from doing this?
They would be losing money without overpriced repairs. That's why they lobby so hard against right to repair.
Even with some kind of right to repair it still seems they're trying to keep you hooked on their resources.
But as you said, service manual + schematics would be great for some people. But companies will fight tooth and nail against it. They lose control over obsoleting older products.
same reason car dealerships want you to only go to them for maintenance
Because it doesn't address the actual problem.
The funny thing about that problem is that it is unsolvable.
The farmers problem is the company is squeezing too much money out of them.
There is no single solution to both problems.