That leaves other evidence that's been looked for. Additionally, the Eurasian cultures that peopled the Americas are all known to have been heavy lithic users.
Somewhere, I have an old stone hand axe. It's really well-made. Not sure where it's from, but I believe it came from a European Stone Age dig, about fifty years ago (probably stolen. People weren't so circumspect, in those days).
The other possibility, is that most of their tools were composed of biodegradable stuff, like wood, bones, and shells.
In Africa, they used wood and raw iron for their stuff (I have spears, shields, and arrows, from there). That doesn't tend to age well.