I think it just doesn't fit into the accepted timeline so it's mostly ignored. This is a common pattern with scientific discovery where evidence that contradicts the prevailing paradigm is ignored and builds up until it can no longer be ignored and causes a paradigm shift. This idea comes from The Structure of Scientific Revolutions by Thomas Kuhn.

I think you're making that up. It is widely known that tools predate humans.

so you're saying archeology and anthropology advance one uncovered ancient gravesite at a time?