I heard a good analogy, but I can’t remember where. I think it was in a podcast.
The presenter said that Google+ is like the BlueRay discs and Facebook is like the good old DVDs that every one has. BlueRay discs were/are touted as the next big thing, better quality, better storage, better everything, just like Google+. But in spite of BlueRay possibly being better, everyone sticks with their old DVDs. They are cheap, good, plentiful and easy. Same with Facebook. Everyone is on it, we know it, it’s easy. Google+ may be better, but why change? Many of us are already suffering from information overload, you’d need a really good reason to add / replace an online social network.