[aaronbaugher]

Also, it's useful to remember that before tractors, there were horses, and the equipment pulled by horses was gradually converted to tractors. With horses, the farmer might sit on the equipment and use reins, or he might walk in front of the horses and lead them. Either way, he had control of them without literally sitting on them. So when the first tractors came along, it probably wasn't automatic to think you needed to sit directly on it. And it was a lot easier to hop on and off them when they were small machines without cabs. They were pretty dangerous, really, with little in the way of safety protection over moving parts, so I can see why people thought a rule was needed to keep the driver on the seat.