D'you think it might have something to do with the state willing to violently require you accept its currency?
Back in medieval and later times, when states were much weaker than they are today, especially economically, and especially small states, people chose which currencies they trusted, and often ignored the coins their local state was minting in favor of other, more trust-worthy coins minted in other places. Those places had no direct power over the people using their currency, and these people were not paying any taxes to them - they were simply choosing a currency they knew was likely to keep its values over the years.
This does happen occasionally in the modern day, with USD-based economies outside the USA, typically in countries with runaway hyper-inflation in their local currency.
Trust is the key.
But also the premise of your argument (taxes and oil) is weak. The value of these transactions pales in comparison with the rest of the transactions. So government enforcement has little to do with the value of USD. It has value, because people believe it, they trust it will be accepted and / or easily converted to the currency of their choice.