Because the dollar is the dominant currency ... all transactions in the world are conducted in dollars.

The United States can print its own dollars. What foreign exchange reserves does it need? . . . . .

But other countries are different. International trade of other countries must be settled in dollars. When you have a surplus, you will also get dollars. These dollars are foreign exchange reserves.

Because the dollar is the dominant currency, the United States has no so-called foreign exchange reserves.

Only other countries have foreign exchange reserves.