Why are dogs so disassociated from their tails?

I’ve noticed that they don’t seem to understand that their tails are part of their bodies, like it’s some alien entity, sometimes to be dispatched.
This morning Cato was waving his tail and knocking some stuff around on the head board. He turned and looked toward the noise curiously. It was obvious he had no clue that it was his tail that was causing the noise.
Why is that?