Comment by teekert
Dogs were domesticated by sort of not letting them grow up. We selected for the ones that retained puppy features into adulthood. They don't loose big eyes, hanging ears, retained playful/less aggressive behavior that is better for living with siblings.
Perhaps the obsession with fetching came with that?
Also, Humans were domesticated by sort of not letting them grow up. Maybe that’s the reason we get along so well.