There is a bit of a misunderstanding here. The ‘actual flesh still attached’ is making you picture something it isn’t. You are thinking this means the flesh has been preserved but with fossils it’s the structure of the original material that has been preserved not the original material. Usually the flesh decomposes away before preservation processes can happen. But the fossil was in an environment where this flesh existed long enough for preservation processes to happen. Preservation isn’t like jerky. Preservation is chemical processes which replace the structures in such a way that the original structure/shape can still be observed. It’s almost like the same idea of making an imprint of something. If you make an imprint of something, although it isn’t the original thing, it still gives you tons of information about it, right? So it isn’t literal organic flesh, BUT they do have a specimen in which they can actually see the flesh. Source a person who is a geology student and learned this in class.

Added info.

Organic molecules have very short half lives relative to other things in geologic time scales, in other words the time in which half the material will have decomposed into something else, so even if you put them in perfect conditions they decompose to their base components given enough time. I believe if I remember right off the top of my head the oldest preserved DNA is dated under 2 million years. Usually the more complex/big the molecule the shorter it’s half life. Even in the most perfect conditions full DNA cannot survive the geological time scales for dinosaurs DNA. We can look for the components it breaks down into, but think about how complex DNA is, if you break it apart into its base components/the puzzle pieces that make it up how can you possible reconstruct that puzzle accurately? It would be like...trying to construct the Empire State Building with only having the materials it was made of. How many different ways could you reconstruct it, how would you know when it’s right or wrong?