Why are historians interested in oral tradtions?

For many generations, native Americans passed on stories and traditions that provided the guidelines for their entire tribe verbally, since they did not have a written tradition. This was their heritage; their memory. So important were these stories that story tellers were selected at a very early age to remember each and every story and to eventually relate each story many times over to the children and adults. This is how the children learned their history and the pride that went along with knowing their traditions.