The magical attraction of metal coinage is that it remains stable, and acceptable, under any condition. Nobody is making any more gold, for example. Nobody is making any more silver, or platinum. These are finite elements, which cannot be counterfeited, or reproduced. Unlike fiat currency, which can be produced to infinity. Now, given the choice of either a finite metal of value, or a piece of paper, which can be easily replicated by government or counterfeiter, which would you choose as a basis of your treasure? It does not take a rocket scientist.