Think of it this way.
Q: Why do you hold USD?
A: Because it’s legal tender for all debts and, actually, the only monetary instrument accepted by the USG to pay my federal taxes. If I don’t have enough cash on hand, I *have* to liquidate my bitcoin (and other cash equivalents) to pay my tax obligations, annually/quarterly.
In this sense, the domestic demand for dollars is manufactured. If I could pay my taxes in $APPL, I wouldn’t have to first pay taxes in the gains, and then pay my tax bill. But the IRS doesn’t accept $AAPL, or any other asset. Only dollars. But, since sitting in the dollar is a melting ice cube, invest it elsewhere, reducing the demand for dollars temporarily.