Just looked at mine,
I would think it's a cheapest way of preventing the locking lever being pulled back through. A pivot is required to enable fitting of the bi-pod attachment lugs, to manufacture a pivot method using fixed fulcrum would be more expensive than drilling a hole in a piece of metal that's already there and then fitting a 0.1 pence copper split ring. I would also suggest that a split ring is used as this will catch on nothing, unlike a split pin, that could and inevitably would catch on grass/heather etc....
Cheap but effective.
TJ