Many products - even corporate products - are chosen for their social signalling implications, not for rational reasons of performance, cost, or efficiency.
Remember "No ever got fired for buying IBM"?
G+ had the technology, but it had no ability to manage the social signalling.
Apple is all about social signalling. That's possibly its primary product. The hardware is just a signifier.
Facebook doesn't have social signalling - it is social signalling. Same with Twitter, and all the other social sites.
Google has never understood how this works. Even when it has a pin-sharp social marketing message represented by extremely attractive shiny people, somehow it never quite makes it stick for specific products in the way that other companies do.
It's so often repeated, but this is silly. Sure, Apple is fashionable, but that is hardly the only reason anyone buys their products. Apple products are good - or at least good enough for their customers - and that is why people like them.
Many programmers here on HN use MacBooks, for example. That's not just because it has a shiny apple silhouette on it.
Actually, in my experience, it's because that's what the company offers them to use at work, and most people just go with the default. I have been told many times "And you get a shiny new MacBook!" And I thank them and mention that I prefer to work on a Linux machine. It is almost comical how many blinking stares I have gotten. It fucking is about the shiny apple silhouette on it. It is 100% about image and not utility ("Sorry! I have work to do and I'm not allergic to the GPLv3!"). Especially because when you buy an Apple, you are paying so much for mediocre hardware at best. I have had better luck with late-model Thinkpads than I have had with MacBooks! They're not magical. Well, not magical beyond that shiny Apple silhouette.
Consider why these companies given employees MacBooks in the first place. (The answer is usually that Linux doesn't work well enough for them.)
So maybe it's not customers' needs, as much as their wants, but close enough. The customers wanted Facebook (because of chicken-and-egg/first-mover advantage and also the good-enough factor), so a me-too competitor just didn't have much hope.
It was similar with Apple under Jobs: they knew what customers really liked and wanted, so they made tons of money even when there were technically superior alternatives to their products.