Fossilization is an extremely rare event.
To appreciate this point, consider that there are 10 specimens of the first bird to appear in the fossil record, Archaeopteryx.
All were found in the same site in Germany where limestone is quarried for printmaking (the bird species name is lithographica). If you accept an estimate that crow-sized birds native to wetland habitats in northern Europe would have a population of around 10,000 and a life span of 10 years, and if you accept the current estimate that the species existed for about two million years, then you can calculate that about two billion Archaeopteryx lived.
But as far as researchers currently know, only 1 out of every 200,000,000 individuals fossilized. For this species, the odds of becoming a fossil were almost 40 times worse than your odds are of winning the grand prize in a provincial lottery.
Biological Science, Second Canadian Edition (Textbook); Freeman, Harrington, Sharp