Earlier quoted context omitted.
You could purchase millions in Bitcoin and other crypto, then sell it to a tether-based exchange for USDT. Then demand it as a withdrawal to USD. Rinse, repeat. No idea how that would end up panning out but you don't necessarily have to accept new tether in exchange for your USD.
The Bitcoin is still an asset they could sell for USD at a similar rate for what you acquired it for.
They would have to liquidate a lot of Bitcoin into USD at once to satisfy a big request for withdrawal, which is a problem since tether's raison d'etre is to provide that liquidity because the dollars weren't there.