Hundreds of US military bases around the world makes sure that no "stupid" leader of some nation makes a decision to switch from US dollar for international trade.
Those who dared to attempt to give up USD for trade, died horrible death like Muammar Gaddafi. It's a direct message to the remaining leaders: "Don't even think about it"
The US reserve currency system allows the US to tax the world, whenever they print more dollars, via oil price inflation. Anyone without sufficient military power who tries to stop denominating their oil exports in US dollars ends up with freedom and democracy being brought to their country. Saddam Hussein switched to denominating Iraqi oil exports in Euros. Gaddafi tried to establish a pan-African gold-back dinar to denominate African oil exports in. And look how it turned out for them.
It’s a stealth tribute system. If you stop paying your tribute, the empire responds accordingly.