But they didn't, the closing and interconnecting of Google's product ecosystem was the beginning of a trend which is now seen across most of their offerings:
The Pixel has silly restrictions as I mentioned. Android apps, Drive, Docs and the office suite apps have gone stale since they came out of beta and lack the commitment to open source that Google once championed.
Even their new HTML replacement, AMP, is heavily tied to Google resources, requiring entirely different implementations of the same experiences between the HTML and AMP versions further handcuffing the buyer to their ecosystem and the buyer's customers to Chrome.
Actually, I just went over there and Google+ looks like it's working just fine. Many parts of it are thriving and there seems to be a lot of activity in communities. Google+ is niche. Just because it doesn't have the ubiquitous adoption level of Facebook doesn't mean it failed.
I really hate this attitude in our circles that unless an app devours everything else and becomes a unicorn, it's a total failure.
Maybe I wasn't clear. My point is that it is Google's attitude right now. If a product is not "a unicorn" they instead rush to something else (Talk->Hangouts->Allo) or kill it (Reader, Wave). Being niche product in Google is just dangerous for that product.