When I activate publicize feature on WordPress to Google+, it always being shared privately. I do not have any idea about that and why.
Let’s see whether this would work or not. It works! Here’s how,
Open Google+ apps and then go to Settings. Tap your account and then click Apps with Google+ Sign-In. Then click WordPress in Connected apps screen. Then change Who can see app activities on Google to Public.
That’s it. Good luck!