1. The people using it don't care if it is, as they may be trying to grift each other anyway, or be using it for short term holding, transferring between crypto accounts.
2. We would only see this on a massive sell off when Tether can't prop up the price fast enough with their reserves (by buying USDT with USD). This almost happened on May 11 of 2022.
3. The Madoff scam went years and years before finally being outed in 2008. Decades perhaps?