More and more traffic on domains is encrypted using HTTPS. This also applies to expired domains, which may have existing links using this protocol and generate traffic using them.
That's why we use the Let’s Encrypt service to generate free SSL certificates which allow us to handle such traffic. If a user clicks on a link using HTTPS, they will be correctly redirected to an offer to sell a domain or will see a correctly displayed domain information page. The condition to keep a SSL certificate for a domain is to direct it to our DNS.