Facebook was the first of this type of social network to get just about everyone to join. MySpace and Friendster and the like got the kids and the heavy web users but Facebook got your mom and your grandma. They got your boss, your barber, and your barista. They got the people who designed websites and the people who never did anything more complex than pointing at a picture on their iphone to launch an app.

It didn't matter if you or I liked some feature or other on G+ (or another competitor) because you can't just switch platforms like you can switch webmail providers. In order to work, you all have to be on the same platform and a good chunk of the potential userbase will simply never deal with switching platforms. How many people in your family or friend/acquaintance group still use their old hotmail (or AOL) email account? Probably not zero.

So even if they did "build a better Facebook" (which I think they did in many ways) it doesn't matter. A nicer layout and some improved features aren't enough to move the entire user base away from the default option. As long as it's a winner-take-all system, it will take a lot more to replace Facebook. It's more likely to become irrelevant than replaced.

Which, IMHO, means Google didn't understand what it was doing when it started G+.