As you can see sometimes the small vehicle turned over. I think the poor cross country performance of these vehicles were their downfall thus the quad bikes as mentioned by dragartist were tried. But not in my time.
As regards the provision of a cage with quick release pins for motorbikes etc We tried something like that during my time at JATE. The big problem was the potential for the pins to bend on impact. Even a small distortion would make it almost impossible to remove them. Anyone who has struggled with the drop nose pins on the a/c role equipment will understand this only too well.