No criticism intended, just a little fun about the system.
My guess is that writers tend to use comments on G+ as an eyes on proof. With sophisticated bloging services, at least you can tell if someone attempted to load your blog, and if they are not using privacy settings & vpn, even something about the person, such are they a repeat or new viewer.
Being circled in G+ means nothing about viewer-ship I've gotten hundreds of circles from people who have never engaged, and probably have never looked at my profile page (because I warn on it that I never circle back unless contacted with the reason for the circle).
Hence +1 and comments are (incorrectly) used to judge traffic levels, when they at best indicate only there are people who want to be felt as being engaged. It's probably one of the weaknesses of the system, and why some of the people whom I follow, but don't engage (because they don't engage back and the trolls on their page do) probably feel they are not getting view and get discouraged.
One way to combat this is to make it easier for blogs to appear as G+ pages, but unless there is a click through to the blog, then the author of the blog may worry that this will depress his blog page readership, which he can track in favor of something (G+) he can't.