Comment by shpx
Dog breeds are not real animals, they're some sort of half-artificial thing created by imperfectly writing some people's desire into another species's genetic code.
If you make an artificial thing that really wants to do some specific thing, like a computer endlessly printing "hello world" millions of times a second, it's not surprising to see it do the thing it was created to do. I wouldn't say the computer "wants" to print hello world, so I don't see the dog as doing what it truly wants to do if it's a genetic predisposition human breeders forced into it. I see the expression of a society of dog breeders and people's idea of a game called "fetch" which was relatively easy to transition a species towards step-by-step using artificial selection.
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?