It's sort of hilarious that it's taken this long for google to realize how beneficial and valuable it can be to add simple social features to their existing products rather than trying to shoehorn a social experience onto everything even when it doesn't add anything in hopes of driving adoption. Pull is almost always better than push.
It seems a far easier strategy to create a social service where identification is a presumed requirement, and then sprinkle a bit of that across all of the other services. By 2011, half a billion users had been trained by Facebook that logging in with your real identity was the norm. After all, all of your friends were doing it.
Thus, Google+ was born. It was the first time that all of Google made a consolidated step toward identification across all of their services. It was a rally point internally and externally, was easily understood, had a clear product roadmap, and opened the door to all kinds of new, stickier products.
I think that the expectations of G+ being a Facebook killer were misguided. Google would love to replace the FB News Feed, but I think it's already achieved much of what it set out to do.