I doubt if Graham peeled off the topic thoroughly enough, and I doubt anyone has ever done that as thoroughly as we have done that in our research. Why do we find (some) dinosaur bones and hardly any ancient "pre-flood" human bones? The best answer is in the logic (as most things).

Firstly:

It is estimated that human habitation started around for at least 200,000 years ago, based on fossil records. DNA patterns show a more reliable period of around 500,000 years. Let's take the average of both: humans roam the earth some 350,000 years.
Dinosaurs could breed and spread during 70 million years (from 245 my-175my) over the whole planet because there was only one supercontinent: Pangaea. On top of that was the period of human habitation shorter: 0.35 my to 180 my => 1 year of humans against 500 years of dinosaurs.
So you would find at least 500 times more dinosaur bones than that of humans. And let's be clear - most dinosaur bones are much larger and so easier to find. How much easier is it to find a dinosaur bone? There are just about 2,000 good dinosaur skeletons found. In comparison, we would expect to find about just 4 good human skeletons. Let's go find them! But where? Can you answer that part of the question now?

Secondly:

Human habitation was less dense than that of the dinosaurs. To estimate how much less is a dubious undertaking. Based on the spread patterns of dinos when Pangaea was still intact, we can make estimations based on different sizes of spread areas to their disposal compared to that of humans who had to deal with restrictions like oceans, climate, deserts, etc. to spread to other continents. Hope you understand that part? Based on this the density ratios are estimated at about 1:8. So 8 times as much dinos as humans per square km.

Conclusion:
When we want to find human remains of long times past, we have to deal with very little probability we will ever find them. The odds to find very ancient human remains (when we include the larger bones) compared to that of dinosaurs is about 45,000 times as bad.


Hope that answered your question sufficiently.