I can list the reasons I don't post here much anymore (with no further comment on the format), many of which you had already guessed, and all of these are in fact interrelated in some fashion:
1) Less intriguing topics than other forums, with lots of newbies while the experienced old codgers are gone.
2) Consequent low traffic compared to other forums / snowball effect.
3) The Facebook factor. ALL forums are dying slow deaths due to the fickle Facebook loving populous of the 2010s, and this forum is hurting more than some others for the above reasons.
This is not to say that this forum cannot survive, or that it is useless. Perhaps it will survive. Each forum has its own unique flavor of community, and this one can become even more awesome, IF we hang around and can attract more people in than who leave. However, I do fear the truth is more like #3 above, and that all forums will soon die, within the next 3-4 years probably.
Anybody else out there remember usenet, like rec.crafts.brewing? I was big into that in the 1990s and early 2000s, but spam eventually took its hold, and with the advent of forums such as this one, usenet is pretty much dead today. I see the same kind of thing happening again now with forums. Something else comes along to take its place, and it's bye-bye forums. It's going to happen. And I can also say, I'm not pleased with Facebook much at all either. It's really all kind of sad. But, at least we'll still have Brulosophy.com, plus good podcasts such as BasicBrewing.com, to keep us going. A few good things like that don't seem to be dying, not yet anyway.
I'll hang around from time to time. But this place is, sadly, well past its prime. Five years ago, this place was booming, and it was hard to keep up with all the traffic. If traffic is what you seek, there are other places out there.... AND the addresses do NOT all begin with www.facebook.com/...