I think this is simply survivors bias for every information transmitted orally. It had to be repetitive, or people couldnt remember it. See here for the Ilyad:
http://faculty.gvsu.edu/websterm/Read_Iliad.htm
> For an oral poet, however, such repetition is not a fault, but a vital technique (Lord 3–67). Repetition is a psychological necessity in oral discourse, which vanishes as soon as it is uttered