A CDN that you have no choice but to use if you want to reach mobile users, otherwise your site will be so artificially de-ranked nobody will click it.

A CDN where active content is extremely limited, and advertising is effectively limited to Google.

A CDN entirely under control of the biggest search engine, who has a direct, a perverse incentive to take as much traffic from you as they can (see info boxes).

Presenting Google AMP as "just" a CDN is very dishonest.