As far back as the fossil records show, we never had claws, we never had fangs, we never had short carnivore intestines or saliva with an acidic pH. Our biology was never meant for sprinting, biting into the hides of animals, digesting bones, or performing other common carnivore / omnivore behaviors. It's not in our nature to salivate at a dead animal, nor do we have the inclination to start digging our noses in roadkill. In fact, as with most docile, plant-eating animals, we have an instinctual revulsion toward anything decaying, because it would make us direly ill to consume it. Carnivores, however, love stumbling upon dead animals and immediately investigate whether there's anything to salvage by rooting through the corpse with their snouts, lapping at any fluids or edible innards.