I don't get it. The Constitution clearly established a monetary system based on gold coins and silver coins. That was the American monetary system for more than 125 years. There has never been a constitutional amendment to convert that system to a paper-money system. Given such, why do we have a paper-money system?

The Constitution called the federal government into existence. Unlike European regimes, the federal government was not vested with inherent powers. If the Constitution had done that, there is no doubt that the American people would have rejected it and would have continued operating under the Articles of Confederation, where the federal government's powers were so weak that it didn't even have the power to tax.

Instead, the Constitution called into existence a government of limited powers. Its powers were limited to those enumerated in the Constitution itself. If a power wasn't enumerated, it could not be exercised, at least not legally.

The Constitution handled the states differently. The states retained the traditional police powers that had characterized European regimes. Thus, unless the Constitution expressly restricted the states from exercising some particular power, the states were empowered to legislate in the interests of "health, safety, morals, and welfare" of their citizens.