I still post on both sites. I think there was some cumulative events which caused posters to leave.
A dominance of discussing left and right politics, which seemed to permeate most threads. This eventually led to having to re-format forums on the HOL
A lack of Moderator time, which Hambo alluded to. Therefore new MODs are fire-fighting without the experience necessary.
New posters, allured by our Premiership status, who don't know how to behave.
And posters like me, who can be a bit *******