Habit, accomplishment, exposure, experience, pressure - not just popular, but also peer. There are plenty of reasons to mod, and I think for some of the modders that have been around a long time - myself, at least - there is very little pleasure left in the activity. It is emotionally trying, and as much as Firebug might acknowledge that he is not obliged to anyone but himself, that is too often far from how we might feel - and this demarcation only grows wider as we produce more works.
Well, Firebug is doing the responsible thing that I cannot, but I hope that he might stay on as a member to this community. There are plenty of observer states in the modding UN