There is not yet a compelling reason to use Google+, and as long as Facebook has the critical mass, that is unlikely to change. It's "Like Facebook, but without all the people". What good is that? The people are why I'm on Facebook at all. Until they start on Google+, I have no reason to leave, and neither do they. If Google wants people to move to their platform instead of the current establishment, we require compatibility more than equivalence. That's tricky to write into software, but did you think changing the world would be easy? Rather than "if you build it, they will come", you get "if you build it second, they will ask Why Should We Change?".
Mokalus of Borg
PS - It's a valid question.
PPS - And the answer is never implied.