I don't exactly know myself but here's what I think.
If you talk about Hacking, certain people will want to know how to do it. Then a Domino Effect will occur, then, before you know it, everyone will know how to Hack and will have hacked their towns. This calls for unfair game-play and a lot of people will start complaining. To some degree, it makes the community look bad.
they're not not allowed, they're just frowned upon because they're worried about seeders and people who use unfair gameplay. I hacked ww on my ds, but that's because the wi-fi doesn't work for my ww game. I don't hack any others though and I certanily do not hack my wii.
Well, the likely reason is because ZettaBoards doesnt allow discussion of hacking, but what admins may not realize is that this isn't the type of thing they are talking about. If you talk about illegal hacking or the actual technicalities of the Wii which could lead to illegal activities for example, thats not allowed. Simple things like cheating on Animal Crossing aren't a bother.
Discussion about hacking isn't allowed because it's against the Zetaboard Terms of Service. Basically that means any forum that uses Zetaboards is not allowed to talk about hacking, along with a few other things.