What were official "memorizers" in the Inca empire required to do and why?

The Inca established their capital at Cuzco (Peru) in the 12th century.

They began their conquests in the early 15th century and within 100 years had gained control of an Andean population of about 12 million people. In common with other Andean cultures, the Inca left no written records. Their history is known chiefly from the oral tradition that has been preserved through the generations by official “memorizers” and from the written records composed from them after the Spanish conquest.

(i know cuz i live there)

what are the issues?