88% of all currency trades are partly in Dollars, with almost all the rest in Euros. If you want to pair two currencies, you almost always have to go through Dollars. Over 80% of international invoices are in Dollars, with most of the rest being in Euros. Even trading between Euroland countries is often done in Dollars.
The Dollar trades on the street much higher than the official Russian exchange rate. If you can get Dollars out of China, past their currency controls, they are worth much more than Dollars at their official exchange rate. The government can try to keep the Dollar down, but the people want Dollars.