Honestly my guess is because many of those cultures used verbal instead written history causing each tribe has their own variations of history and lore (think game of telephone but through generations and hundreds if not millions of years) so there's no concrete story that everyone holds near and dear like cultures that passed on written history that has less flaws and variance in storytelling (due to translations and interpretation of text) thus appeals to more people.

Tldr; text based storytelling has a backbone/source despite translation and interpretation errors. Stories passed vocally lose their source almost immediately, either through the teller dying, or losing their mental facilities, or not having a plan in the first place so the story would've been told differently by the same person even within a span of a few days or depending on their audience.