They easily eat nearly rotten meat, their stomachs are designed to handle it, skin, bones (marrow from them), other parts people don't eat are used to feed dogs on farms.
Dogs that are bred for food are living food waste recycling factories, kinda, they eat everything that can't be eaten by humans, in return they "produce" edible meat.
And don't forget that dogs aren't mass-bred. Number of dogs that are eaten is relatively small.