G+ lost because Google forced G+ to every Google account. Post something to Youtube, you silently created a G+ post. Upload something to Picasa, you silently published the photo to your G+ newsfeed, etc. - quite toxic. And have they learned from their Google Buzz (G+ predecessor)? Nope, same behavior.
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.
G+ wanted to be a rendezvous for all social/sharing activities on Google, and it turned out that many users didn't like it. Would G+ have fared better if it didn't force G+ onto every Google property? Maybe? It's easy to do armchair analysis, but hindsight is 20/20.
I don't think Win10 is that bad. In fact I think they fixed the MS account OOBE that was bad in Win8.1, making the option to use a local account much more clear.
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.