I'm assuming your forum post count wasn't increasing because you were always posting in boards/sections/individual forums which grant a user no points for posting, namely the Forum Games and the Newcomers' sections.
There isn't a way of letting post count increases register from posts made in these forums without AP increasing either. Thus, we'll have to live with no points being gained from these sections.
As for why points aren't given for threads in the Forum Games section, all the forum games used to be in the Tavern and back then there was a lot clogging up the Tavern. If people could freely earn points from forum games, we'd be seeing a whole lot more spam.
