Nothing prevents a browser from doing this. But it does nothing unless websites respect it. So far many websites haven't been cooperative, as evidenced by the amount of shitty cookie consent pop ups we all have to deal with.
Sure, but we're speaking of a kind of standard (RFC or more specific one).
In this case, compliance is in the law: albeit not perfect and people trying to game it, you have to comply or be fined (if you do business in the EU).
Compliance is already in the law: Accepting and rejecting cookies needs to be equally easy, otherwise you don't have consent for processing personal data. That's how they got these fines.
