It was, for the most part, regular DRM and proprietary data/hardware format stuff that is common across industries.
The very high cost of the equipment if it were bricked for license violation, and the very narrow windows for being able to use the equipment (if you need to call John Deere and have them re-enable your tractor you've just potentially lost out on an entire seasons revenue) were also big factors. Many of the farmers that we talked to were fed up enough that they would have risked it, but between our own direct legal risks, and the risk to our reputation if our customers equipment started getting bricked, was enough to stop us from moving forward.