I'll take a pass on what I'm sure would be a satisfying discussion about whether a few molecules in the rock means something is "not entirely fossilized." I may have overstated the case; it's hard to tell from the several writeups I checked.
Nevertheless we're left with rock containing a few organic molecules and "cellular components" for dinosaurs, versus dry leather and edible meat for mammoths. Do you have an explanation, or are you too stupid to realize that it's obvious you're running away from the question?
The explanation is simple enough. The mammoth died approximately 3500 years ago and the dinosaur more like 5000 - 50000.