They disconnect it because a) any bouncing leads to shut-off at most inopportune times and b) they cannot ever leave the tractor just for a moment, such as to move an obstacle or something they forgot. Not good to keep turning off and on the engine.
It’s nice in theory, but as with most safety items, there is still a cost-benefit ratio to consider.
I have a neutral switch on my tractor that the seat sensor is wired into. If it is in gear and you unweight the seat, it shuts off.
If you are bouncing out of the seat and causing the tractor to shut off, you are driving waaaaay too fast..