In a bid to grow its user base and peddle awareness of Google+ as a social media platform, the mothership has been integrating it into a lot of its other services, like Google Play Games for instance. It looks like Google is finally settling on the fact that Google+ has failed to catch on, and it will be decoupling the social network from Google Play Games starting in 2017.
In actuality, this move was announced by Google early in 2016, but is only coming into fruition now. Google has been very straightforward in pushing Google+ wherever and whenever they can. But this is stopping now. Last year, Google decided that they would no longer require Google+ accounts to make YouTube comments. In February of this year, Google announced that any new Play Games accounts would have player IDs that are not tied to Google+. And just yesterday, they have announced that all Google+ integrations would stop starting in February 2017.
One of the main functions of the integration was so that you could see game stats of people in your Google+ circles. There also other logical features such as social leaderboards, gifts, and real-time multiplayer based of your circles in Google+. But the fact of the matter was, nobody was really using Google+ that much.
So starting in February 2017, all games that require Google+ social data will not get any. Google will also stop using the social network as a sort of virtual back-end for social integration. Google is opting now to go with the more universal (and simpler) Google Sign-In API for authentication. That means you only need a Google account, which far more of us have and use rather than a Google+ account.