> It seems so unbelievable to me that there are enough people that are a) John Deere equipment owners/renters and b) capable of debugging and patching issues in a C++ codebase for these stories to keep appearing.

There doesn't have to be any overlap between these groups of people. The issue here seems to be that some mechanical parts that are easily replaced, are not accepted by the controlling computer, unless it is authorized using specific administration software. Basically, ink cartridge lock-in, but for tractors.

To circumvent the restrictions, no farmer has to know C++, they only need a pirated version of the software to integrate the replacement parts into the system. So what the farmers want is not the ability to arbitrarily modify the software running on their equipment, but simply a way to do purely mechanical repairs on their own.