I touched on this before in my rambling. Google botched it, not the product itself as the initial offering of G+ was actually really really good. Far better than Facebook, a return to basics in a clean interface with Circles. Groups being a feature Facebook later added.
When Google launched G+ it was actually one of two new products the primary one being Google Accounts. Before that point you needed to use a Gmail account to sign up on any of Google's services and it made everything a big pain when you had more than one Gmail.
Now with a single Google Account you could sign in to Google's entire ecosystem, including all of your Gmail accounts at the same time. It also came with a free, ad-free, totally simple, you-don't-have-to-use-it social network called G+.
Google should have marketed this all honestly. Instead they started talking up G+, and hid Google Accounts underneath it. This was a huge mistake. The general public felt like they were being tricked, because they were, albeit far less nefarious reasons than was assumed. Nobody wanted to give their name, to sign up to G+, and therefore rejected both G+ and the Google Accounts system.
This compounded because Google really needed everyone to switch to the new account system. Otherwise they were doomed to continue supporting both Gmail authentication and Google Accounts authentication forever. So Google began pushing for people to create Google Accounts, as you would imagine. People then saw this as Google trying to force them to give their full name, trust was already gone.
Amazing to me people trusted Facebook over Google because at the time Google so far had a very good record protecting private information. Now that's all gone of course but at the time they had an incredible amount of good will which was seemingly not reciprocated and now Google is a slimy gross privacy succubus the same as Facebook is. Probably they just threw their hands up and said 'fuck it'.
Google tried to further reduce complexity in their myriad of different platforms. They now had two social networks G+ and Youtube. G+ was going to eventually absorb and replace Youtube, it would have been pretty elegant really. The first step was to have the Google Accounts system absorb Youtube accounts. People resisted this again because at this point good will was gone. Eventually Google gave up on everything.
Now G+ is a cesspool of tacked on features, advertising, just a bad smell entirely. It did have a lively base for a short while. Things really went downhill after the Youtube consolidation because G+ suddenly had what was notoriously one of the worst communities on the internet, Youtube comments.
Google has I believe still not successfully moved everyone over to Google Accounts. Youtube was never successfully merged into G+. G+ is pretty much dead at this point. Nothing went well at all and now Google has to support a million different things that all barely work.
Meanwhile Youtube hasn't seen a facelift in about a decade while Google figures out what it wants to do with it.