I know a ton of people who set up a G+ profile and I found both the web version and mobile app to be superior to Facebook's offering. Plus they had better image hosting and they had good text/video chat before FB updated theirs.
But in the end it comes down to critical mass of users (and particularly, non-early-adopters) on Facebook. You might get your other peers to try out a new service if you're into trying out new sites/services but unless you get everyone to make (and use) a profile the way most people seem to at least have a Facebook account, you're stuck maintaining two profiles on two sites and switching between them depending on who you want to share that update or photo or link with.
In the end it didn't matter if they had a modestly better site or mobile app because nobody wanted to post to two sites. And since, unlike email, these things don't operate on any sort of standard protocol, you can't just switch your client and let grandma keep using her old one so it fizzled as a FB competitor.
(I still use it for several niche interest groups though. Also I think circles are vastly superior to whatever Facebook has for granular control of who you share something with.)
When fb came into existence there wasn't much of a competitor to it, so they focused on making it easy to use and stuff, later, when g+ was being created they misread the entire picture. At that point fb had become a platform or was becoming a platform. Currently, FB has different users, some use it as a buy sell group, some for messenger, some for playing games (APIs) etc
g+ didn't focus on good things, just beautiful UI doesn't mean you win, you have to differentiate yourself, they should have gone this way, start a private beta, build a terrific API for developers, so devs will flock to your platform and build apps on it, plus the circles stuff, it is great for geeks like us, but not so much for my grandma, who doesn't even know what google means. Plus, g+ takes an awfully large amount of time to load on slow network. Overall. Plus they don't have an end vision.
What pisses me off most is that there is no clear alternative if you want to keep your data portable between multiple brands/devices. Microsoft often works poorly. Apple only works on Apple. The alternative is a hodgepodge of services (SimpleNote, HERE maps, EverNote, etc) that requires tons of accounts.
I'd love an open and honest answer from someone up high in the org chart at Google on that. Better yet, just an acknowledgement of it and how they're going to stop doing this in the future. If they were a startup with 200 employees under the age of 30 I'd understand it, but they're obviously waaaaay beyond that stage.