The soul is the only thing that can not be replicated; each person has a unique soul. Even a clone body given life has a soul different from the original and its own copy.
When it comes to the soul, it means they are their own beings without any connection to the original; even when the clone gets transplanted with the memory of the original, the clone will still have its own agenda and tend to break free from the control of the original.
This is the reason why mages prefer to use homunculus instead of a clone body: homunculus is like creating a blank body to house a mage's soul. Cloning a body is like creating another human being with the same structure and memories but with a different soul than the original. And the process of a soul occupying a clone body is something that is impossible to stop either.