The point here is that the archaeological record seems to indicate that it's like one day we simply 'woke up.' Whomever was fortunate enough to experience such a mutation first would have had a tremendous competitive advantage. The degree in intellectual advancement is such that they would have probably been significantly better at just about everything -- most importantly in surviving and spreading their genes. Now take this person and what would likely have been their vast number of offspring. They could effectively take over the world. And I suppose, in a manner of speaking, they did.
Either that or the kinds of artifacts we look for simply don’t last longer than 70k years on a planet like this.
Or, it’s just rare enough that, when combined with the cost of excavation and the fact that scholarship builds on scholarship, it’s just not the kind of evidence scholars are going to dig far past we’ll established boundaries to find.
Lots of possible explanations for the data.