Why can t healthy dopaminergic neurons be moved into the area of parkinson s affected neurons to treat parkinson s disease ?

Not so simple: Most of the dopaminergic neurons end in the substantia nigra of the midbrain, originating in various deep brain structures. These nerves are already affected by the disease. Unaffected nerves of course still remain but remain connected to brainstem. So outside nerve cells (from another source like stem cells are needed) nerves don't like to be moved around anyway, because they often die.