Even if Dexes could be completely anonymous, which they can't, it is simply the case that you cannot swap for cash fiat without routing through legacy mechanisms. In 100% of cases, getting cash in exchange for crypto involves KYC/AML regulation and surveillance.

An anonymous dex (if one could exist) could issue a card to HODLers that when used to make purchases could debit your crypto HODLings, yet compensate the merchant with fiat. This isn't possible, despite being obvious and having been tried. Without a bank account, you're not getting fiat from your crypto.