Not that it matters any more, but if you work for Google and wonder why ignored all those invites, it's because you, Google, insisted I change how I share my use of your products as a condition of joining Google+.
Before Google+, I used a variety of your products - blogspot, youtube, search. You know that the same person was using all these services - but the world in general doesn't, and most importantly, none of them were tied to my real name.
Then, to join Google+, you wanted me to "convert" my account, and attach my name to everything.* I was not interested in that, so I diligently stayed away. For Facebook, on the other hand, I knew going in that it would use my real name. (I still waited as long as possible and only signed up to avoid becoming a hermit.) Since I knew my name would be attached from the start, the way in which I share has always been somewhat sanitized.
Because you, Google, are so many things, you can't be a real-name social network, at least if you insist that I retroactively claim ownership over everything else. Sorry.
* Even if this isn't true, this is what I got from all of the media coverage, discussion, and your own promotion. If I understood this all wrong and could have keep using the other services separately and anonymously, then it's your fault for advertising Google+ so badly. That's sort of sad, given that advertising is your business.**
** IIRC they did change this eventually, but by then Google+ was already an obvious failure and it wasn't worth creating an account.