Publishers can, and should, always make visitors aware of how many third parties are positioned to see all visitor data. We are, unfortunately, a long way from

Publishers can, and should, always make visitors aware of how many third parties are positioned to see all visitor data. We are, unfortunately, a long way from this being normal. Even as third parties doing things like running CDNs or doing TLS termination for other reasons has been pretty thoroughly normalized. Though offering it as a Firefox extension could be an interesting exercise. I think publishers view AMP as a question of their sovereignty and choice. Since it's their website that's being potentially served by Google, it's their choice to make. There's absolutely a lot of room to dispute if this is the morally correct stance, but I also think it's not wildly out of line with other questions publishers weigh in choosing what they serve and how.