And bluntly, no one uses forums.
Caveats aside, I agree, which is part of my point/complaint. I don't want to sound like I'm merely whining about how things were better in the old days, but in some ways they were. The problem is that social media sites are a dime a dozen these days and people only have so much time to commit to online activity. Social media is also easier, in that it takes much less effort and is all (if you want it to be) self-directed, meaning you don't have to conform to any forum rules, etc.
The end effect is that you can post in detail if you want, but there is a drive towards the bottom. Quick fly-bys gather more +1s, and are just as easily dismissed in the flow of information. That's not to say there isn't long-form content out worthy of consideration, but I don't think social media in its current form is very good at corralling it. I get more value out of the weekly Story Games email (which is actually pretty good!) than I do a week's worth of scrolling through posts on G+.
I don't want to necessarily blow up G+, but I do think that it's much more of a crap-shoot subject to social gamesmanship and emotional whims (i.e., Usenet). For me, that's a personality clash that I have a tough time reconciling with the way I like to spend my time.