Facebook has, and has long had, a real name policy. If you want a reason why Facebook succeeded and G+ didn't, you'll need something that's actually different between them.
Facebook was designed from the outset to be an online platform for your real-life friends. G+ should have been an online platform for your online friends, but then it mandated that all of your online friends must now need to know your real-life name.
Are you saying the real-name policy was retroactive? I wasn't aware of that. If that was the case, wow.
And the Youtube integration was also the immediate end of the real-name policy (which was really more an "no unusual name policy, because people got blocked for having an unusual real name, whereas plausible pseudonyms were left alone).
But you're right; it was a stupid policy, and they should have known that right from the start.
I have somewhat similar feeling about the upcoming Win10 launch, and in near future a lot normal user will learn the hard way why they got Win10 in exchange for the current Win7/8 license.
Simply don't outsmart your user base.
Everyone knew what Google was doing was monumentally stupid on so many grounds.
There was widespread criticism over the real names policy and linking across properties.
[1] http://thinkprogress.org/economy/2015/07/04/3676529/truth-be...
[2] https://www.facebook.com/chris.cox/posts/10101301777354543
Keep in mind, Google already had experience with two social networks they owned. The Real Names policy probably didn't fall from the sky as an idea without merit; they might have had reason to believe that without enforcing real-world names, the resulting social network wouldn't get Facebook traction.
Google instead tried to shoehorn existing users with a different culture. Perhaps they could have created a separate service with different expecteations and grown that, but they seemed to feel entitled to a create a short cut to success at their user's expense.
When you're providing a platform, you can't afford to be opinionated.
How is that different in kind from what Google offers to consumers?
Google also offers binary blob data storage/sync, and a phone OS. Is that key?
In particular, when people came to gmail in the first place, they were using it as an email service. When they came to youtube, it was as the world's largest collection of videos. They did not want these conflated.
You could list all those items for Yahoo and for AOL as well. But Youtube is distinctive in offering a huge collection of searchable videos. You name it, it's there, until it gets taken down by contentID or made unavailable in your country. Can you even search for videos on Facebook?
Google offered a lot of totally unrelated things, from a phone OS to a video site, a search engine, and a social network which did incorporate some stuff on its own (hangouts and photos were well integrated and not really a problem as far as I can tell).
Suddenly introducing connections across all those different sites, so your mail contacts end up on your phone, your Youtube posts on Google+, and identities that you want to keep separate get merged against your will, that is stupid, harmful and a betrayal of their users.
And I have an `active' facebook account with a fake name and people I really want to `follow' or people I let in.