90 percent of Google+ user sessions are less than five seconds.
Their own stats seem to back this: people arrive by mistake and immediately go somewhere else
It's like following a search result to experts exchange on the age of stack overflow.
The more infuriating part is that it doesn't even work on mobile FF. So the few times I accidentally click on a G+ link from my Google assistant feed, I don't even get the benefit of seeing a post with just a link to the real content.
even when i don't arrive there by mistake, i typically leave after less than five seconds - people would link to posts on G+ and before reading them i'd have to click through full-screen interstitials introducing me to the "new" G+ redesign. and i just didn't care, so i'd leave.