I believe you're right when you say "just that G+ didnt innovate,or try to have a fresh take on social networks" - G+ failed because of that, and that's the whole story. They can't force people into something that's not interesting, new and/or revolutionary.
To be honest, i don't know the answer to that question either. But I'm guessing there's a good reason why they decided to provide the solution in this form.