It HAS a social network but it ISN'T a social network.
And identity layers are more popular than you'd think. Most apps these days, allow you to sign in using either your Facebook, Twitter or Google logins. It saves you having a different account for every service and it provides secure access through a reliable platform.
Facebook popularity is declining with key markets. Especially teens. This is why they bought Instagram and WhatsApp which are strong in those demographics.
By all accounts, G+ popularity is growing. Anecdotal evidence, but my 15 year old niece recently deactivated her Facebook account and activated her G+ account.
But Google+'s social layer doesn't need to pass Facebook in content usage.
Google already has the most popular social network in the world. It's called YouTube.
I'm sure FB is becoming less popular for many reasons. The privacy settings are shit, the UI changes (and shit) every six months or so, and most of the things you
used to be able to do on Facebook are now being brought out by separate services and made much better.
Twitter is better than status updates and I've grown to love it to get my news from it. Instagram is the one place everyone goes to share their photos now, and despite being bought by FB and being able to be integrated with it, many people still prefer to use IG over sharing pics on Facebook. We know this because people now use the phrase "I'm putting this on Instagram." SnapChat has a role in there somewhere too.
I think all these individual services, collectively tore Facebook apart. Even I've deactivated FB to study and I don't really miss. I do reactivate every so often just to check, but I really could live without it and not really have many missed connections. I still stay in touch using Hangouts or email. I still get my news from Twitter.
My point being, I don't think something with the structure of FB is going to last long. Whatever G+ is, I have not even accidentally stumbled upon a use for it. Others can use it, fine, but it's not for me.
The problem I have is associating my real name with it. I need to use my real name for my GMail account, but Google wants me to use it to post a YouTube comment. I'd rather not have my account associated with the comments section of a YT video that has gone viral, even if I'm not saying anything vulgar or embarrassing. I can not imagine using my Google Account to log in to another site. I've seen sites ask for Google info to log in but that's just one more thing I'd rather not associate my account with. It's the same reason I don't use Facebook to log in with any other service either, lest my name be used on something like Spotify where it can take note that I "favorited" Koon Jamz 42 playlist.
Sure, it's easier to just associate everything with Google, but I'd rather not. I think I might have my Flickr or Box.com account and maybe Dropbox associated with Google. That's it. I trust those sites and those sites I actually really
need some connection with Google to access documents or send files to others. I wouldn't use FB to even log into SH.
Google needs to set some boundaries for itself. Not everyone wants their name plastered on a YouTube video of a chimp playing with his scrotum.