Maybe that filter was designed more to deter the crab-eating macaques from turning the airbox into a larder - a crankcase contaminated with a few particles of random airborne dirt (or bits of filter element) is a trivial matter compared one filled with mashed-up carapaces and odiferous crab-parts, after all. Though I allow the hole might allow one or two crabs to be inserted, it would complicate matters after that...