I think to expound a bit more:
1. New threads were met with "do a search." Kind of hard to keep content going if all that is said is "do a search" instead of re hashing a concept with the goal of coming up with new ideas.
2. If said person did a search and bumped an old thread, that wasn't always met with positive results either. It was almost as if some of us just didn't want to talk about it again. lol
3. An influx of how do I make a Sturgis mix (giving him his own forum was a good idea IMO).
4. IIRC James Murphy got out because he had less time for it and got sick of all of the above (plus you know actually physically sick, poor dude), plus IIRC there was a thread where people where being twats, I can't fucking find it under the new skin though. I think he also didn't like some of the off topic content.
5. The rise of facebook and youtube. People are just not doing forums as much anymore. I'm experiencing this with other forums as well. I left HC like 3 years ago because it got so dumb it wasn't worth it (that and the 2 software upgrades were just fucking bad).
6. Andy Sneap only posted when I first started on the boards, but he didn't often (I remember when he put up the Chimera toms, that was pretty kickass). I'm guessing he is just a busy dude. TBH I have no idea if he even has much to do with this forum anymore other than we discuss his work from time to time.
7. Misha, Lammert, Joey, Toxic Grind Machine (sorry I may not be remembering his U.N. right), JeffTD, Glenn Fricker, Ermin, etc... were posting a lot more work. We had some quality work being posted and that of course made more more interesting content. I'm guessing most if not all of these guys have better things to do these days.