Because machinery with batteries are too easy to start.
What?? you're parents never dragged you into one of those places when you were little and you just happen to find yourself alone in the seat of a backhoe and wondered, just what would happen if you turned that key? and pushed a few levers this way and that way, and wondered if it would really make it over the tractor display????
And to continue my thoughts . . . Not to mention the fact that we don't want folks like Hiram running amok with a backhoe in a crowded auditorium.
"Courage is not the absence of fear, but the realization that there is something more important than fear."