If some random Bob were to print some new money and try to exchange it for resources, no reasonable person would comply. Because this Bob can just keep printing money and concentrating resources, while everyone else has to work. If this Bob were to find a big stick, he could force some smaller Bobs to use his money. But on the international market, his money would still be next to worthless. Because everyone knows that Bob can keep making money whenever he wants.

This is where all these complicated systems, processes and agreements come into play. They create an appearance that Bob can't arbitrarily print money. Obviously, he still can, he has the printer. What he doesn't have, is the biggest stick. This stick is owned by the government. And Bob will either do whatever the government tells him, or he will be bopped and replaced. By a more obedient Bob.