Same reason everyone not Facebook hasn't yet given up and declared defeat? This isn't Highlander: there can be more than one. Google+ has plenty of active communities of people who choose not to use Facebook. Nothing wrong with that.
In fact afaict G+ has a very different vibe from Facebook, so I think of it as an alternative to Twitter rather than to Facebook - it generally feels like a public discourse rather than a "share my baby pictures with homies" type vibe. Except you have more than 160 characters (or whatever Twitter's new limit is), so conversations can flourish much better.
There are multiple writer communities, DIY communities, Yoga/meditation groups, sci-fi fan groups, etc., and a lot of android apps use their G+ communities as their support forum + user communications page. (And those are just the ones I know of.)
For whatever reason, these kinds of "I don't use it and my friends don't use it, so why does it exist" type posts and comments - which seem to happen repeatedly here - are posted disproportionately more so with G+ than any other minor but thriving network/forum /thingamagick.
That's also how I tend to use it. I think the main issue was that it was positioned as "hey, we built a better Facebook!"
This was somewhat accurate IMO since I prefer the layout, features (many of which Facebook added shortly after), and granular sharing (which Facebook most certainly lacks).
The main issue I ran across was that Facebook continued to dominate in the space because it was the first to gain a critical mass of users across a wide spectrum. MySpace was big with the younger crowd but typically you didn't find your mom, your boss, your barber alongside your friends and drinking buddies.
Facebook was the first big one where eventually all of your relatives (even the ones who typically didn't care about "techie" stuff) and acquaintances built a profile. So when G+ came out, most of my friends tried it out and quickly realized that they would still need to cross-post things to Facebook if they wanted to share with all of their contacts and not just those who like trying out new things.
Without a common API or protocol, there was no way to just pick the service you prefer and go on with your life. With email, I could switch from Hotmail to Yahoo to Gmail (or even roll my own server) in search of the right setup for my preferences. I could still email anyone who refused to give up their AOL account or who used their work email.
Facebook-style social networking requires everyone to be on the same platform in order for it to work. So instead of some people sticking with Facebook while a big chunk slowly migrated to G+ or other competitors over the space of a few years, you ended up with lots of people trying out G+ and getting annoyed that only a few friends bothered to read/reply.
So now it's mostly used as more of a subreddit-style thing where you can have topical groups rather than personal friends and acquaintances. I still do think it's a shame they couldn't "build a better Facebook" because it would be nice to have a few options for that type of thing. But unless some new player can convince absolutely everyone you know to migrate, it just isn't happening anytime soon.
While I don't use G+ for anything, a good friend tells me that's where the role-playing game community is centered. He writes blog posts about an RPG he's developing, then links to them from his G+ account so that people with an interest will see them.
I'm a regular Google+ user and I find it incredibly valuable. The fact that there are fewer people on there is actually an asset - the people that do use it do so because they have some topic they're interested in that they're discussing with other interested parties. There's a lot of mathematicians, scientists, and authors. In general, the average g+ user is much more knowledgeable than on any other site.
Also, the actual features are super valuable. You can create collections with varying levels of privacy for your posts. I use some private collections to take notes, and post more well thought out content in the public versions of those collections. The collections help me organize my thoughts, and I can see different ideas emerging over time. I have a collection to talk about software engineering practices, for example.
Also, being able to create private communities is nice. My wife and I have a private community where we share things about our daughter - photos, things we want to remember, things she's learning.
Same here, I've tried feedly and a variety of local clients but it just didn't have the same charm. Now I just pop open HN, my automatic Google Now feed, and reddit occasionally.
I still have the Reader bookmark next to Gmail's. Once or twice a year I click it accidentally and get angry all over again. It serves as a reminder to not put all my eggs in one basket.
All those who relied on Google for things like Reader are much better off running their own news aggregator (the Nextcloud "News" [1] app being a good example of such). Especially given the latest spate of censorship by the likes of Youtube (-> Google), Facebook, Twitter and others I'd say it is irresponsible to put this task into the hands of an entity like the aforementioned. Irresponsible both because there is no way of knowing what they decided to filter out of the news stream and because it makes it even easier to profile their users by tracking what you read, for how long you read it, etc.
Because millions of people are using it ? I use it daily, I'm subscribed to ~40 communities mostly tech and photography. The signal/noise ratio is way better than facebook. I've not used facebook in several years so maybe it's better now but it did not add anything to my live, quite the contrary, G+ does.
If you haven't heard about this person's wife using Google+ it's a little bit of anecdotical evidence that it's doing its job of supporting communities rather than generically connecting people (like Facebook).
The user interface remains outstandingly bad, but I've never seen clickbait links or scammers on Google+.
Some elements seem unnecessarily complex, but I actually like Google+'s UI. No one I know uses it so therefore I don't either, but I do like the look of it.
Personally, I haven't used google plus in awhile but when I used it, it wasn't for the social networking of people I already knew, but it was for following communities w/ topics that I liked.
The problem I'm finding with Facebook right now is I don't want to spam everyone with science-y articles or to offend/bother people who might not care for liberal view-points.. just because there are so many people that I know that are on their network. Also, I'm too lazy to create groups to target my posts with. It ends up just being a photo-dump with maybe written posts once a month + mostly keeping brief tabs with family+friends.
When I first started on Fb, it was addicting posting things I could reference later or writing long-ish essays or being ridiculous with friends (photoshop wars).
I think this is it. They knew their best way of beating Facebook was going to be incorporating Plus as tightly into Google as possible. If you remember, it even integrated into Google searches for a while in a very obvious way (though they rolled back how visible that is).
I'm not a developer, but I'd imagine it's not a single thing they can remove, that it's mixed into of every team's code, all over the place.
At my last job we used it internally (part of the G Suite, I believe) for employee profile pages, especially since we used Hangouts and Gmail a lot to communicate.
An important feature is OAuth2. Google+ is an identity provider. In other words, Google+ is perhaps used a lot more than it seems. It's like an underground infrastructure nobody sees.
I always thought they should morph/change/add circles as a method to do authentication, authorization and enterprise group permissions.
Imagine an Enterprise IT worker creating a Resource Circle called "Salesforce" or "DropBox" and a user group called Marketing.
I would want it to work for inside private resources as well as public resources. Same thing with user groups. Groups of employees, contractors and outsiders.
Not, that no one is using it. I am using it daily and at least the several hundred people I follow do so too, there is quite a big community in tabletop roleplaying games for example. But google has for years only done what they always do to their products in recent years: add more and more whitespace while taking away features. And of course, this drives people away. So it is getting slowly quieter over there and of course, all it takes google to finally close it down is one engineer finishing his 20% project for the "next big thing" to replace it.
This will be a sad day for many communities on google plus, but at this stage in googles life, nobody should be surprised by products just going away.