Since many exchanges use USDT and USD interchangeably, the endgame is for arbitrage bots to bid up the exchange rate between BTC:USD at legitimate exchanges to match BTC:USDT at Bitfinex. This allows Bitfinex to transfer the BTC they bought with Tethers to legitimate exchanges, sell them for USD, and transfer the USD back to themselves. They could care less about anything beyond that.

That's what I believe too, but once thing I don't understand is you would think by doing so they would depress the price on USD exchanges, and eventually cause the price to decouple between USD and USDT, but that doesn't seem to be happening this time.

Exactly. With USDT, your aim is to buy crypto low and sell them high and become bigly rich, THEN you cash out (which is the end game). It's just greed.

Notice that the general confidence in the crypto ecosystem (HODL culture), and in Tether itself (it's just a FUD, it's been so many years and nothing have happened) contribute to the desirability of USDT. Also notice that when I say cash out, I'm not talking about redeeming USDT, but buying crypto then selling the crypto on an exchange or OTC that has an off-ramp.