More that nobody buys any USDT with $ at all, and then Tether announces that there are two billion new USDT, which are then used to buy BTC. The trick is that

More that nobody buys any USDT with $ at all, and then Tether announces that there are two billion new USDT, which are then used to buy BTC. The trick is that lots of exchanges don't have any way to convert from crypto to real currency at all so use USDT as a stand-in, USDT's supposed backing 1:1 with $ means it's a stable place during crypto volatility, and it's next to impossible to actually get $ from directly exchanging USDT.