The risk is actually the other way around. A page can't access data in an extension, but extensions with full permissions (most of them) can access anything on any page.
Hacking a popular extension is one of the easiest routes to fully compromising millions of users (and every account they own). People are generally unaware of this danger, but it's much worse than ads or tracking.
Hacking a popular extension is one of the easiest routes to fully compromising millions of users (and every account they own). People are generally unaware of this danger, but it's much worse than ads or tracking.