over thousands of years, we caused them to evolve qualities that make them lovable.

a hungry wolf pack would wander over toward a family of cavemen; the cavemen would feed and protect the wolves that were a bit friendlier, a bit more outgoing, a bit cuter, a bit more willing to protect them from other predators; meanwhile the uglier, asshole, aloof wolves would starve to death or get eaten and fail to reproduce.

repeat for a couple hundred thousand years or so, and the cute, friendly, lovable, loyal dogs are the ones being selected for, and a symbiotic relationship develops between man and dog.