It's called "Audiogon", not "Musicgon".
Off hand (and I got zero data for this one), I'd guess that music is discussed as often/more often here than audio gear is discussed on most music forums. There's a fair bit of music discussed tangentially in the equipment forums, but the question seems to be addressing the lack of activity on the music forum. I spend 90+% of my time there because the posters here strike me as a great resource, but why would you expect the music forum to be high volume on an equipment web site?
Or, to put it another way....
How often is music discussed on guitar or drum kit web sites? How often is literature discussed on e-reader web sites? How often is driving discussed on sports car web sites?
None of that means that the visitors to those forums are necessarily misguided in their priorities, it probably just means that they visit those places for the purposes that those places were established.
Marty