Gary Illyes, the man to blame at Google for the HTTPS algorithm, shared a "small" analysis Google ran on HTTPS URLs. It showed that 80% of HTTPS URLs that were eligible to be included in the Google search listings, were not because the webmaster canonicalized - on purpose or by accident) - the HTTP version instead.
Google wants to show the HTTPS version, but if you communicate to Google to show the HTTP version, they will. But Google really wants you to show the HTTPS version and 80% of valid HTTPS URLs are not being shown in the Google search results because of the configuration.
Gary wrote:
A recent, small scale analysis we ran showed that more than 80% of the HTTPS URLs that are eligible for indexing (i.e. no crawl issues, no noindex, all's good), can't become canonical because website owners don't tell us about them. They use the HTTP variant in their sitemap files, in the rel-canonical and rel-alternate-hreflang elements, even though the HTTPS variant works mighty fine.
Gary added that if you go HTTPS, go HTTPS on all your pages saying, "use HTTPS URLs everywhere so search engines can see them."
He is fighting the fight!
Forum discussion at Google+.
