They started with the largest sizes and it has been trickling down, for somethings that makes sense; there are tractors out there the size of mining equipment that need perimeter cameras to see the ground. They are roughly the size of a two story house.
Lawsuits and court decisions specific to motor vehicles have shaped manufacturer responses concerning the ability of the private sector to access what was proprietary intellectual property. Similar challenges in the off-road equipment sector are decades behind the motor vehicle industry. There is certainly proprietary IP incorporated in some tractors built in the 1990's controlling transmission clutch packs, electronic draft control and certain engine monitoring systems. The question of when did this all begin has no across the board answer, you need to research specific machines and applications to develop individual answers.
Good ol feature creep, a salesman's wet dream.
Workshop manuals are just that, workshop manuals. You need the diagnostic books for whatever series machine you are working on. Kubota I can not really speak to as they don't really have issues that often and all I've had to do is read and clear codes. New Holland on the other hand you can do all kinds of stuff, read and clear faults, recalibrate clutches, replace components... Sure there's things you can't do, but you can do a lot of stuff without a laptop.
