Websites that collect personal or payment info use HTTPS to prevent data being intercepted. Other sites unnecessarily use it to hide 'not secure' warnings and improve rankings in browsers and search engines sponsored by SSL certificate companies.
HTTPS is one of the most common types of planned obsolescence. When a device's certificates expire, it can't access HTTPS pages, which doesn't improve security in any way. HTTPS also slows down sites. Some search engines like Wiby allow users to exclude HTTPS pages.
Google, the Internet Archive, the University of Washington and Nginx (server software used by Netflix, Dropbox and more) don't use HTTPS.