Imho not exactly regarding the USDT scandal many years ago. It was not audited because there were not enough proof about every single USD "covered" by USDT. At the end they found the appropiate amount of USD in a bank in the Kayman Island.
The main problem with stablecoun that they are issued by a centralized corp/xchange. In case of USDT the Bitfinance, or BUSD it is the Binance. And Binance is not so sympathic to the US authorities, so they want to "overregulate" the Binance in the US.