Now that's the point here. Even if you can't set up a legal battle over what's made in a video game, it's still just as bad to do such a thing. People work hard to make user-generated content (like the dream towns in ACNL), and if people steal their work and get the credit for it, the original creator would be upset about it since he/she made the town, and she doesn't get any credit at all. This is wasted work.
Even if my town isn't protected from theft, I don't share my dream town on tumblr. And since I blog a lot about my town, people will know that I am the original creator of my town. I'm even re-blogging about it on my site. So I'm unprotected (like everyone), but thieves won't get what they want from my town.
The other big deal about dream town theft is that they're using an unauthorized and external device to steal the town. The same device they're using is also known for ruining ACNL in other ways, as the same company (Datel) made other devices that ruined the previous games.