"Soft mouth" means they don't bite what they're retrieving. Spears and arrows don't need "soft mouth". Plus a dog can be trained to "point" to something or just run it out. Why waste a spear or an arrow or a bullet when you have a pack of hounds that will run out the coon, fox, etc? Let the dogs do the work - there's no need for a spear when the deer collapses from exhaustion.