Those stablecoins are permissioned by the issuers just like dollars are permissioned by the Fed. And if the issuers of those stablecoins transmit dollars on behalf of their users, they're under the purview of the Fed, who can restrict the usage of those dollars.

The entire point of Bitcoin is not to use fiat, so issuers of dollar stablecoins on Bitcoin are bound to be captured and brought under the Fed's control, just like Tether, which complies with government sanctions despite claiming to be decentralized.