Actually the thing I like most about this forum is being able to talk about old games casually without creating a thread and announcing it with a "LTTP" thread followed by a dozen or so posts where people acknowledge the existence of the game in some way. Why someone would post on gaf and not here? there are more people with different tastes that post at a higher frequency (look at any icecream thread).
As for posters I liked that don't post anymore, I think most of them were already covered. Don't know why they left and it's not really my business, but not posting worked out for them, good for them. Personally, I post forums to talk about games or other hobbies because I don't have that outlet in real life.