I think they cynically understand that it helps prop up demand for T-bills and bonds. And if there's another bull cycle with BTC halving in 2024-2025 they probably wouldn't mind the underlying bond purchases that will result with Tether and other stablecoins.

Simple answer: you can't regulate scams. Stablecoins are the scams of the scam (fiat shitcoin). That means they will regulate fiat (again). Stablecoins are a fucking joke.