As a counterpoint to this, my childhood was on a farm, and pretty much was straight out of a John Mellencamp song. We didn't have hired hands, were not dirt poor but certainly not "well off". We pretty much did all the work as a family - including fixing the tractors to some degree. Well, honestly, my dad did that and at best I watched. That might not be your experience, and I respect that, but small family farms still do exist in some parts of the US. I can see why these folks would want to fix their own tractors. For one, do you know how hard it is to get a tractor that isn't working to a dealer?
As for John Deere being a greedy corporation or just trying to make an honest buck - you can look at it either way. The fact is that tractors these days are large very expensive pieces of machinery that are generally not purchased sans financing - so the initial cost vs monthly cost is just a matter of which pocket the money comes from.