Because...?
(Yeah, I *know* I'll be sorry I asked...)
Real simple, none of the dating methods in use doesn't rely on guessing or assumptions that cannot be verified in anyway or falsified. IE, it isn't science, it's a belief system. Just like Core sampling of the ice packs. Science can't determine with any reliability how any given artifact arrived where it was found or what conditions led to it. The most they can do is try to look smart when pontificating about how it props up their belief system.
When you date freshly formed lava flows to anywhere from 10s of thousands to millions of years old, one can say with authority that the technology is nothing but highly sophisticated manuer. It's better to say "I don't know it's age" than to lie or bs people that you do when you have no basis for making claim.