August 2014, Google released an article sharing their thoughts on how they planned to focus on their “HTTPS everywhere” campaign (originally initiated at their Google I/O event).
The premise of the idea was that every website, regardless of what it was doing, should be communicating securely between point A and point B. To help motivate users, it went right for the carotid artery by making it a ranking factor in search.
December 2015, Google adjusted their crawlers to start start prioritizing and indexing HTTPS pages by default. If you had HTTP / HTTPS, they would start giving more weight to your HTTPS pages.