The reason GDPR doesn't standardise a consent mechanism is because GDPR isn't about websites, its about data protection. It applies to offline companies just as

The reason GDPR doesn't standardise a consent mechanism is because GDPR isn't about websites, its about data protection. It applies to offline companies just as much as it applies to online companies. GDPR has nothing to do with cookies (that's a separate directive), but is about personal data, personally identifiable data, the use of this data and user rights over their data.