Why do all audio forums on the internet seem "dead" ?

Activity varies with the topic, MHO.  With the advent of 'PC-fi', there's interest in adapting one's current system to the 'new standard of standardness'; that's where there's the typ. 'Q&A' happening.  Those who've made a substantial investment already seem to have hunkered down and will only make a move 'sideways' to something that's either come on the market at a price point they can live with or 'trade across' to something they've lusted for that's become available used.
The 'hi-end' market has become so esoteric and pricey that having to choose between a nice pair of monoblocks or a car 'update' or covering the kid's college tuition or co-signing for a house makes matters moot.
I spent the bulk of my time on the DIYA forums of my choice, because that's what I can afford and where my primary interests lie.  The bulk of the new gen market is 'into' the iThing/PC/Bluetoothed/AV interconnectability realm, and 'hi-end' to them is what they have NOW.  Irregardless that us 'old timers' listen to this stuff and shake our heads in disbelief or at worse disgust.  Until and unless they hear something that will make them pause and ponder, that's where the 'bleeding edge' IS, and will remain, the Moore's Law moving target.
I'm not surprised by this.  If I didn't know better, due to 'age and experience', I'd be part of that chase too.  Now I'm just picky as to what I let into my life, and the level of extremism I'm willing to go to.
I've consciously set 'the bar' a bit lower, as age and knowledge has superseded mere gadget lust.  Age, because I don't have 'dog whistle' hearing anymore.  Knowledge, as in recognition of the previous and that copper can be made only so pure and the pursuit of more zeros right of the decimal point becomes more of a bragging point than a unbiased A/B test in a listening environment that looks like a NASA facility....
...and I don't want one of those, either...anymore.  I used to have a pile that was occasionally referred to as the 3rd member of the household and was just short of having a manual to get it up and running.  The SAF was reached at that point....
I have Something Similar at this time, but it's not in the 'general living area'.  The GLA has something far simpler, but still has too many remotes for her taste; fortunately ONE does suffice for most daily distractions...
Time has changed the playing field;  forums for the new field are Elsewhere.  Those of us who care about such are Here.  We're in decline.  'Twas always thus.  Maybe we can be the shoulders that get stood upon if we're lucky....

Actually since there are relatively few new audiophiles, you know, what with the Walkman, iPod, iPad and iPhone generation and given the lack of interest and or means to pursue an (increasingly) expensive hobby in the midst of a raging recession/depression, actually a series of them, I would opine the real average age of audiophiles doesn’t obey the Atkinson formula and to be around 64.

I could be handy, mending a fuse
When your lights have gone
You can knit a sweater by the fireside

geoffkait, you could again, be on to something here. Doing a very quick, very non-scientific study of my local audio group, the most stalwart, hardcore of the 300+ mailing list would probably fit neatly between JA's and your #, yet closer to yours. And I would agree that the market hit (2008) and continuing hangover, have left this hobby to waste for too many very logical reasons. Sad, but true. And we may well be the last remanent. 

doing the garden, digging the weeds
who could ask for more?

I read the big two audio mags for 10+ years and then let them lapse. I've visited the big two fora for the last 10 years as well and find interest (my own) lagging as well. Been there done that in both cases. The freshness wears off, the same posters soldier on with, in may cases the same well worn agendas. The same handful of trolls keep popping up with the latest disingenuous topic of the day and the same crew of responders, oblivious to being played, it seems, chime in as if on cue.

10 years ago I might have logged on to tell you how my first adventure with full system cable cooking went (hooked everything back up yesterday after 100 hours on the Dharma). But now, I realize, I'll just as likely have to start defending myself from ridicule as much as sharing any insights. Don't get me wrong, I don't cringe in the corner in worry over internet reprisals. But why bother.