The Jivaro of Peru ruse up against their Spanish oppressors. Apparently the Spanish governor of the region was very hungry for gold. He got a bit pushy torturing and killing to get compliance. The tribes banded together, took his fort, melted the gold he had demanded and poured it down his throat. The written record was preserved some couple hundred years later (I seem to recall a priest was present for the confrontation took notes and drew pictures). The oral history in the tribe had lost it. Cool story, lost because that tribe has a tradition of blood feuds which causes oral traditions to be interrupted.

My point is that oral tradition requires an unbroken chain and events often conspire to break generational tradition.

The written word is a hedge against the loss of oral history. There’s nothing to say we couldn’t have both.