User blog comment:ARevolvingDoor/Nexon's Connundrum: Are they really doing nothing?/@comment-1375749-20111203011955/@comment-1375749-20111203163326

the idea is that it's just simply cheaper to patch the hacks most of the time rather than taking them to court
 * red tape
 * the costs (given their apparent hesitation suggests that it's not worth it, or it's a cloak and dagger operation)
 * success probability (what are they going to sue them with? copyright infringement?)
 * as for the above I'm not sure what they can sue the hack sites with but it's probably not going to be powerful enough to do the job in many cases

Also think of the other companies with similar issues (e.g. Jagex of RuneScape fame putting up with botting, granted the recent bot nuke really did the job there)