The whole idea is that the government gives you a cryptographic token that proves you are over 18, but that token can be used anywhere. They don't get to say what websites can look at it, because...how would they.
If age verification was an open standard, we could hope for competition so that we could jump ship from a bad actor. If one blocks our access, we would have alternatives. In theory.
Not so with a centralized government-mandated service.