Submission + - Google's insistence on forcing all sites to HTTPS is misguided (this.how)
A lot of the web consists of archives. Files put in places that no one maintains. They just work. There's no one there to do the work that Google wants all sites to do. And some people have large numbers of domains and sub-domains hosted on all kinds of software Google never thought about. Places where the work required to convert wouldn't be justified by the possible benefit. The reason there's so much diversity is that the web is an open thing, it was never owned.
Many of these sites don't collect user data or provide user interaction, so the "risks" of not using HTTPS are irrelevant.