That is not Tether's stated business model. To issue 1 USDT, Tether is supposed to take in 1 USD from someone, and hold it safely in an account.
Their stated business model is taking a 10 basis point or $20 fee (whichever one is higher) when someone buys USDT with USD. https://tether.to/fees/
The likely fraudulent business model would be printing USDT that aren't backed by USD, purchasing cryptocurrencies with it, and then pumping up the value of that cryptocurrency to realize gains.
Done right, they might even make enough money with such fraudulent trading to eventually have the cash reserves they claim to have. Maybe at that point they'll finally complete their first audit. Their site still makes the shocking claim "subject to frequent professional audits" despite having been fired by their auditor.