Ask HN: Why doesn't a GDPR HTTP response header exist?

Is there a reason why the browser makers/W3C/whomever haven't created a gdpr-approval-required header, or something similar? Seems like pointing to a txt, html or xml file and blocking cookies until it's accepted would be a much easier way for everyone to comply with GDPR.

Then again, I admittedly don't know much about how these things get implemented so I may be way off base.