Because we are talking of two different things; the skills needed for survival and history. Which do you think would take precedence? I don't know the answer, in bountiful times there may be time for history, in lean times the stories may be for basic survival. I will tell you one thing, survival is reliant on experience, knowlege, or training, there is no guarantee any or all of it will result in a happy ending, but "none of the above" is guaranteed to end badly. On a priority rating of having to memorize stuff, the real life relevent lessons learned and conveyed are the key to survival. Actual history can end up bastardized or embellished because memories either fade, events were forgotten or were considered irrelelvent, or there were other pressing matters at the time. At least when it is written it can be taken in context of the writer and the times, when it is oral is is merely a story.