[jkhdigital]

Countries started using the dollar because the US was the most powerful economy left standing after WW2 and thus the only trustworthy issuer of currency. The petrodollar system helped things along even after economies were rebuilt, as it meant that anyone who needed oil (i.e. everyone except OPEC) would also need to keep dollars on hand to pay for it.

After decades of this, we've reached the point where the US Dollar is so deeply embedded in nearly every global supply chain that everyone needs it all the time. I don't think it has anything to do with being transparent about financials or unlikely to default; it's just accepted everywhere and has a better stock-to-flow ratio (i.e. stability) than the alternatives.