It's not the interest rating of the US$ which makes the US Currency so popular. It's the falling currencies of the nations not living under Euro or Dollar domains.
Do you think that this is one of the reasons why countries wish to be independent from the US dollar? We don't live under Euro and Dollar domains and our currency is getting weaker but despite everything, people want to be near to US and EU as much as possible. It's a little bit strange but my country tries to become more dependent on US and Euro instead of getting rid of it. The reason why we want this is that US and EU countries are rich. After the fall of the soviet union, lots of people migrated to the EU and the US. They managed to build a better life in these countries and they also managed to send money to our country to help their mothers, fathers and relatives. Because of this, our country sticks with the US dollar and I feel sometimes shocked when other countries try to get rid of the dollar or Euro and join BRICS.
It is not just about Soviet Russia, all the poor people in the world who have something to provide, ended up in bigger and better nations. Plus, resources do matter, and military do matter as well, political stability also matters a lot. Even when presidents were assassinated, law still got uphold in USA or most of Europe, whereas in Africa, or Asia, and specially in Latin America, there were chaos ever few decades, that made them even poorer.
No matter what you do, no matter what a politician can do, some poor African town with barely one source of clean water, can't get the improvement, even a thousand years ago Europe was better, it is just geolocation that makes it so hard, it is not just personal improvement alone.
People say white people in south Africa build a great life for themselves whereas blacks didn't, so it must be race or culture, but they forget, white could take the resources and send it to Europe and get rich, blacks can't, those type of differences caused USD and EU to end up being valuable, because the nations are powerful.