Yi, first of all, dogs were not all bred from one type of wolf. Breeding a wolf with a wolf gets a wolf! To imagine that all dogs were bred from wolves is ridiculous. Humans would choose a pair of wolves with different characteristics, and the result would be cubs unlike either parent. Such selective breeding over a few thousand years has resulted in the enormous variety of dog.
But make no mistake; every dog is a wolf! All the instincts of a wolf are still there.
You ask, why are they so submissive? Because they are pack animals; and pack animals follow a leader, usually an Alpha male.
The owner of a dog becomes the Alpha male of the pack.
Dogs can be very friendly, and seem to be submissive. But beware! A dog can revert back to a savage wolf in seconds!