The problem with Google+ is that people inside Google saw the things that were going wrong with it and the executive team didn't listen. A lot of them were punished. People were fired over RN advocacy, and the person who tried to save the Games product from failure had a manager push him out through various abuse-of-process tactics enabled by their ludicrous "perf" system. (Interesting fact: Google has two weeks every year where nothing gets done because everyone-- not just managers-- has to drop everything and write performance reviews.)

Google now has huge internal morale problems because of Google+ and the culture is falling to pieces. That, in my opinion, is why it will never succeed.