Wild horses don't stand in a box or small pen 24/7 on soft, green pasture. They are out w/t/c several miles a day over all sorts of terrain, sand, rock, hard dirt and that is what wears the hoof down.
Endurance and cart horses usually need shoes to stop the wear, as the ground or road may wear the hoof down too quickly.
Horses with bad, weak, damaged feet don't survive.