Why is Hermes the gos of shepherds?

As a boy, Hermes became a shepherd. He won the Caduceus (staff of shepherding) from Apollo, who previously owned it. The staff was supposed to be able to put flocks of sheep and cattle to sleep. Mortals later worshiped him as the god of shepherds because of this ability. You can read about the story of Hermes in the book "Hermes the Olympian" available as an e-book and paperback on Amazon.