They buried them in shallow graves or even did sky burials where the body is left for the carrion eaters to strip the bones and then they collect and bury the bones. The concept of burial practices themselves have only been around for approx. 120,000 years but that doesn’t mean they were burying them all in one location 6 feet deep. It’s just scattered randomly in shallow pits/caves.
When we find any signs of long term habitation from that time, we often do find bones there. But there are really just not that many sites with that depth of information available.