This is because most scientists have already decided that evolution over millions of years is 'a fact'. So, when new fossil evidence is considered, the idea that evolution could be wrong is never contemplated. Take for example animals with backbones. Vertebrates were once the only major animal group not found fossilised in the Cambrian system of rocks. The eel-like sea lamprey and hagfish are examples of agnathans and they live in the oceans today.
Lampreys are semi-parasitic and use their mouth to attach to other fish.
So, fish appeared much 'later' in the rocks than many other animals, and this seemed eminently logical to the evolutionists. They surmised that it would take much longer for chance and natural selection to 'work out' how to construct animals with backbones than it would shellfish or trilobites. An extra 125 million years would be more than enough time, they thought. 7 Similar finds were later reported from Australia. These are dated at some 470 million years.