My guess is, even if there were some elegant, widely-supported standard for machine-readable privacy policies and even if browsers had some dedicated built-in API for privacy consents with some really polished and frictionless UI, you'd probably still be bombarded with popups begging you to click the "consent" buttons on that UI.
The problem is that it's not a technical problem, but a political. No matter how technically elegant your spec, it doesn't change anything about the underlying conflict of interest: Website operators want to collect personal data and show ads, while users want to keep personal data to themselves and don't want to see ads.
So trying to solve this via any kind of web standard is asking the website operators to act against their own interests. If you have no enforcement or incentive, you will end up with a standard that is either toothless (P3P, DNT with opt-in) or simply ignored (DNT with opt-out).
GDPR (and the cookie law before) do have enforcement, which is why web sites can't ignore them - instead they fight back with a barrage of popups.
The problem is that it's not a technical problem, but a political. No matter how technically elegant your spec, it doesn't change anything about the underlying conflict of interest: Website operators want to collect personal data and show ads, while users want to keep personal data to themselves and don't want to see ads.
So trying to solve this via any kind of web standard is asking the website operators to act against their own interests. If you have no enforcement or incentive, you will end up with a standard that is either toothless (P3P, DNT with opt-in) or simply ignored (DNT with opt-out).
GDPR (and the cookie law before) do have enforcement, which is why web sites can't ignore them - instead they fight back with a barrage of popups.