How did I develop bunions?

A bunion is not an enlargement of the bone.  It’s the normal bone, but in an abnormal position.  If your foot is not as stable as it should be, there is a muscle imbalance, as the muscles and tendons try to stabilize your foot, but can’t.  Instead, they move the bones and toes into an abnormal position.  Your instability is hereditary.  Blame your parents.