Some could be booby trapped and if they have been left lying around who knows what condition the HE material inside them is like... it could have sweated and be rather unstable... it is better (safer) to just destroy it.
Looks like they were looking for UXO and expended munitions, so they were not poking their rods into every square cm of ground... they were looking for fired or unfired ammo on the surface or freshly impacted the ground...