I dont know why it is not possible to trade with USD on Bitfinex or Bittrex, but it is a Problem for me. I sometimes would like to sell my Coins for $ and then rebuy BTC when Price Drops. If i want to do so know, then i have to sell my BTC via Local Bitcoins or some other Websites, where I cant rebuy BTC immediately, because they offer only wire Transfers.
I hope somebody can help me :/