Why? It’s not inherently valuable beyond a handful of industrial/electronic uses.

It has the precedent of societal agreement going back thousands of years longer than literally anything else besides food and prostitution. If the world started over from the stone-age, people would be using precious metals to represent value all over again. You don’t need it to make sense, you just need a social agreement, and that doesn’t happen with just anything that can fall apart or decay or be found easily.