Where would these real USD come from if USDT is worthless? Why would a holder of USDC or DAI accept USDT in return if USDT is worthless?
Why anyone holding usdc would exchange one for a usdt at par is a question I don’t have an answer to, but it’s happening en masse.
One possible explanation is that you have more pairs available for other cryptos with USDT than with USDC on some exchanges