Because there is a fiscal deficit which requires borrowing, which means that new money is created. If the new money were spent only in the USA it would cause pr

Because there is a fiscal deficit which requires borrowing, which means that new money is created. If the new money were spent only in the USA it would cause prices to go up a lot, so the money goes overseas so that the price increases are more moderate (arbitrage). Why is there a fiscal deficit? Because politicians want to win elections. If the fiscal deficit were ended then mathematically there could not be a trade deficit.