I remember back in the day when I got a Facebook account, the colleague next to me asking: so what is this Facebook thing all about? Not very many people had heard about then. But for those family and friends that had, it was a great way to keep track of everyone (staying updated without, you know, actually engaging in social activities like phoning or e-mailing or meeting up). Which was great from the introvert standpoint. Back then, not much thought was spent on the more sinister intelligence-gathering capabilities. Ads were not really obnoxious.
Then it slowly, very slowly, turned up the frog heat. Today it is a place where the few social updates that you are still interested in, are buried between reams of mindless meme reposts, ads in which you have not the slightest interest, and algorithmic down-prioritisations.
Be the time G+ came along, I guess a lot of the more tech-savvy people had become clued-up and wary about the data-collection. I for one didn't want to give more data to yet another company, and strenuously declined to enter details, or use a G+ profile to log in to any of the few other google services I used. I also linked-out, have never twittered, instgrammed, whatsapped etc.
Giving people back a non-data-farmed, non-ad-soldout experience would have needed to be an indispensable part of their required killer feature set. But that of course didn't serve their purpose.