Because the integrity of the hoof is affected by the effects of physics, mechanics; balance, ground pressure, movement, angles, leverage, etc.
Because one prescription, or Rx, for the hoof is to correct the balance and angles to positively effect ground pressure and minimize the degenerating effects of leverage. The hoof must work in a mechanically balanced way so as to not overly and/or improperly stress any one piece or part of the anatomy.
Because the hoof is a “smart structure” and is able to “fix” in many ways.* I am fascinated by the way I have seen flat, thin-soled horses develop thicker soles and better concavity with proper care. Because the hoof is at least partially formed by the physics of its use and environment, and nutrition, imbalances in any of these can cause the hoof to deform and become more damaged. “Fixing” many of these issues may also “fix” the foot.
* Great talk by Dr. Debra Taylor from Auburn University: Is the Hoof Smart? Adaptability of the Equine Foot