If we didn't eat them....what would they be for??? Haha. People in this world, beleive it or not, keep animals like that as pets. My Friend has two cows, three chickens, a goat, and 4 sheep who are all just pets used for 4H, and she doesn't sell them to slaughterhouses.
Plus, if they aren't being eaten, then they prob wouldn't be here. People who breed, will breed and raise specifically for food. So if the demand goes down, so does the supply. Thats the beauty of supply and demand!!