I did not know this. Is it for theft prevention, or more like a deterrent to e.g. would-be clandestine arms manufacturers. I'm aware CNC machines can be quite pricey, but they otherwise seem like an impractical target for theives. At least a tractor has wheels.

Yes and we don't like it.

And it's a very bad no good awful thing.

Stallman is extreme, but he got that part right. DRM and other bricking mechanism are not our friends.