As they should be
All impact caused xx extinction hypothesis fail in one regard, and it's the same issue the Noah's flood people have. Where are the bodies?
The fossil record should be littered with bodies of extinct animals at the time of impact, but no where is this the case. With the YD impact, most species in most areas went extinct thousands of years after the fact (and not coincidentally whenever man showed up). With the Dinosaurs they were long gone before their supposed extinction level impact. Of course the answer to this is more & more epicycles impacts.
The YD impact hypothesis is just a bad attempt to keep alive the Noble Savage myth.
The remains of animals very rarely become fossils. The conditions that create fossils from bones only exist in certain geographic areas during certain climactic conditions and geologic conditions that have to remain stable for many thousands of years.
And then finding fossils is an even more difficult proposition. A lack of remains from a tiny slice of time 10k years ago means nothing.