Google pretty much always roll the best parts of the tech into other things when this happens though. Google Docs as we know it today contains some of the best technology pioneered within Wave.
I think Google+ was actually a massive success, and I’ll explain why. This is my opinion but from what I’ve learned and observed, this is what happened.
The idea that Google+ the consumer product social network was what Google wanted was somewhat of a red herring. Sure - they would have been happy for it succeed, but the lack of resources put into it over the last 4-5 years points to the fact that it did it’s job. I’d argue that G+ did it’s job within 2 years of launching.
Before Google+ what many folks might not remember is that most Google services were silo’d and independent of each other. Nobody used an account for Search or Maps. Gmail was a different account to YouTube. Amongst other things. There wasn’t a centrally linked “Google Account” like there is now.
More importantly, none of these accounts were fundamentally linked to user identity. This is why Google caught flack for initially forcing users to use their real name on Google+.
Over the course of the launch, Google+ became your Google account. YouTube then became linked to the Google account via Google+ etc. This went on for years before they were relaxed. Literally maybe 4 or 5 years between introducing these policies, “real name” verifications, etc, and then relaxing the policies.
By that time, having a centralised Google account that was linked to your identity became a de-facto thing for most users. It became the norm, just like with Facebook. The Google+ system became used as a platform for signing in to other websites to verify the account just like with Facebook.
Once that became the norm, and all formerly disparate Google services were centrally tied together by way of Google+, the job was done. The “social network” part could have been put to pasture right then and there, because it wasn’t the aim behind the project.
For me the writing was on the wall after Vic Gundotra (who spearheaded the project) left Google in 2014. He really was the driving force behind the project. I suspect that had he been as personable as Sundar, he could have been CEO.
By the way… Google Photos, which is pretty much universally acknowledged as the best mobile Photo storing/sharing app (I even know many iOS users who use it over the default iOS Photos app) also started life as a feature within G+ before being spun out into a separate project.