Actually - at least according to young earth creationists - their remains (or at least of some of them) should be found as fossils in the same layers as some dinosaurs, since according to many YEC, dinosaurs lived up until then and the chief reason dinosaurs were fossilized was the immense pressure of the flood waters. So human fossils should be right there next to dino fossils.
I suspect the lack of such is caused by the grand evolutionist scientist conspiracy rearing its ugly head again.