Because after 50,000 years there should be any Carbon 14 left. But if you had read the article you would have learned that many of the fossils that have been dated as very old, have significant amounts of Carbon 14 which shouldn't be there. Often 100 times more than should occur based on known sources of comtamination.
But you have been told why there's carbon there. I've been on several threads before with you. I know you've been told repeatedly. Creationist amnesia amounts to lying.