I can see how this evolved. You sit near the humans, don't act aggressive, they give you food. You make puppies that follow the same plan. You give up the dead end profession of providing security. The parcel guy might also give you food, you never know!
What I don't get is how their other instinct evolved: "I must bring this tennis ball to master, and master must fulfill the social contract of launching it"
Sure, I can see how hunting for stuff makes you want to run over to something and pick it up. But what about the "throw the item 40m so I can run after it?" Why would that have a purpose? Why is the appetite for doing this insatiable, to the point where you are advised not to do it with small puppies who might hurt their hip development? Is it all just an extension of the juvenile stage, where play is important?
Labs have also become the dominant breed of dog through exceptional salesmanship. I bred my lab, and she had eight puppies. We advertised them, and not a single one of the families that came to see one decided against it. The mom would bring a puppy to the family, and as soon as they were holding a puppy, you could tell by the look in their eyes that they were sold. It's like she was saying "Hey, you look like nice people, buy my kid! He'll love you forever".
The puppies at that stage are already able to look deep in your eyes, and can already do the "oh hey, that's some interesting food you got there" look, and they already love a belly rub.