It was only a failure at what Google wanted it for - displacing Facebook as the dominant social media company. IMO, they failed primarily due to network effects, as in they can't bootstrap without some killer feature to get people to switch over from Facebook. Circles probably didn't help here, since the ultimate effect is to reduce engagement, when they need to maximize it to have a chance of displacing Facebook.

Probably the big risk for this thing is that nobody wants to keep track of separate websites for dozens of individuals, most of whom only post something they can see once a week at most. You need to aggregate all of those updates from dozens of people you know into a single website and build a feed, then you have something that probably always has something the user might find interesting, and all in one place, so they'll actually check it regularly.