This is partially what the P3P standard was defined to help with, and the only browser that every seemed to do anything mildly meaningful with it was Internet E

This is partially what the P3P standard was defined to help with, and the only browser that every seemed to do anything mildly meaningful with it was Internet Explorer. All IE did was refuse to set/keep cookies if either a P3P header wasn't provided or it didn't match the "user's preferences" (which the user never looked at or understood), so it just ended up causing headaches for web developers who at first tried to figure out which parts of the site's privacy policy matched the codes in the header value. When they found out that didn't work, they just copied the value of Google's P3P header. So many sites' privacy and data collection policies didn't match what they were asserting in the P3P headers, because otherwise, the site didn't work.