The Middle Eastern countries -- like many of our trading partners -- generate large trade surpluses with the U.S. due to their oil wealth. The U.S. buys oil from the Middle East, and pays them dollars in exchange. These people can't eat dollars, so the U.S. currency doesn't do them any good except insofar as they can use these dollars to buy other things. So they purchase U.S. Treasury bills, U.S. real estate, race horses, expensive cars, and other such things. One thing they also like to do is acquire reputable global corporations like P&O Ports in those lines of business that these countries value highly (global shipping, in the case of the UAE -- for some fascinating reasons that I could describe in detail if anyone wants to get my take on it).
If these countries start running up against bureaucratic opposition in the U.S. to these financial deals, they have a huge disincentive to sell their oil for U.S. dollars. With the euro now competing with the U.S. dollar as the preferred currency for international trade, the last thing the U.S. wants to do is provide them with any kind of incentive to start pricing their commodities (primarily oil, in the case of the Middle East) in something other than dollars.