Why did early human ancestors keep dog's ancestors?

I have also read a story long time ago about a guy who raised a wild fox. The fox was loyal to him until one day it left him for another fox. He was quite upset about the "betrayal" until he cooled down and thought it was probably the best for the fox.

As for the process of domesticate the dogs and other pets,
You call it human friendly, I call it submissive lol.
I guess the so called domesticated animals are just the repeat selection of the most submissive ones. Submissive could be in the genes.