The dollar has maintained its artificial value for two major reasons:
1) Oil transactions are done in dollars even when the US is entirely not involved in the actual deal. The buyer has to go buy dollars artificially boosting their prices to pay for the oil which then the seller usually invests somewhere else but does not convert. As oil deals outside of the US are in the trillions of dollars, the artificial boost to the dollar's value is immense.
2) With so many reserves consisting of dollars, central governments are afraid of a significant decline in dollar value as it would punch gaping holes in their balance sheets. Thus they enact policies either to keep the dollar up or their currencies lower. Again, nothing to do with transactions with the US. Some banks have wised up to this fact within the past decade and actually have gone about reallocation of their serves into a larger, more diverse basket.
Note: both of these are entirely artificial and in no way represent real economic transactions.