They can also peg the value using BTC. Basically they just buy using their dollars/fiat some BTC, deposit it to exchanges, and then using some simple bot beg th

They can also peg the value using BTC. Basically they just buy using their dollars/fiat some BTC, deposit it to exchanges, and then using some simple bot beg the value of the USDT to USD with bid orders. And vice versa, they can have some USDT on exchanges and have ask orders so that people can buy USDT using BTC. If there are more buys than sells, then they withdraw the BTC and sell it for dollars/fiat. They don't need to do that on that many exchanges to have effective peg to USD. However they of course still need traditional bank accounts, and they need to trade the BTC on OTC markets or somewhere else.