Toenails are protective, especially the large toenails, which bear the brunt of force from jogging, footballing and many other sports. The nail sits right on the bone of the terminal phalanx, and is closely associated with the distal interpha langeal joint. Toenails especially are prone to repeated microtrauma over the years from footwear, sporting injuries and changes due to arthritis.
Fingernails suffer from whatever traumas we put our hands through—chemicals, soaps and detergents and, for some, the added insults of nail salons cutting and dissolving cuticles, using harsh chemicals to apply and remove polishes, false nails, acrylics and so on.