You just haven’t practiced:
[E]ven adults show cortical plasticity after some simple muscle training. That is, piano practice caused the amount of brain devoted to voluntary muscular control grow. So although you may not currently be able to flex your ring finger or control your individual toes, there’s no reason that you can’t learn how! Amputees, for example, can learn to be quite dexterous with their toes.
The Dish 