We've had plenty of cease and desists from Nexon and the like. We once had to hide the entire Combat Arms section (removed from front page and renamed to combat armz) just to prevent a lawsuit from Nexon. We usually just wait these things out, eventually they forget about us. There have been a few games which we had to stop supporting but I've forgotten which.
I would assume companies would rather go after the hacker making the hacks than a forum that distributes, There is a lot of forums that are specifically for game hack(and most of the time when a hack is released its downloaded and spread amongst many forums) so it would be easier to slap a nice lawsuit on the hacker to discourage anymore hacks and maybe just tell the forums to remove the hack. But this is all just a guess nothing for sure.
Honestly Nexon doesn't give a shit about these hacking sites until they start losing money (which they haven't).
Big Corporations don't worry about this but they still pepper these sites with legal suits just so it seems that they care.