The content is served from Google's servers according to Google's (not publisher's) privacy policy. While Google cannot alter the content, it sees the unencrypted HTTP request. I don't want neither Google nor publisher to control contents of my address bar.
Google already knows the unencrypted contents of the page, and they know you clicked on a link to it (from their search results page). The signed exchanges system doesn't reveal any information to Google _or_ the publisher that they don't already know.
Your browser controls the contents of the URL bar, not Google or the publisher.
