I’d like to explain why we used the (A)GPL license for PokeNet, and why I continue to use it for other projects.
Reason 0: Because we wanted to.
The authors of the code can choose the license they want. It’s that simple. We believed that keeping the game closed was just bad mojo, and that there was a lot more to gain by open sourcing the game. We wrote the documentation. We debugged the game. We bugged the game, sure, but in the end, as a developer, it was our choice for the license.
Reason 1: Because we wanted to force forks to share back their code
Forks, Downstream, Leeches, however you want to call them, what we wanted was simple: That our efforts would not be closed up by some high school kid with a keyboard and our code. That’s the main reason we chose GPLv3 and AGPLv3 (For the Server) as our licenses.
We documented as much as we could in what little time we dedicated to the project.
How to compile the code, how to run your own server, how to contribute to the game.
I know, most of these articles are long gone. They were posted in forums that have been abandoned/deleted since the C&D, but that does not justify taking someone else’s GPL code and closing it up.
Reason 2: It makes contributing easier
By having your code open to everyone, you’re inviting others to fix bugs in the client or server that might otherwise bother them, or perhaps implement features, or help translate things. It starts with a patch, but they might become regular contributors. That’s how I got roped into PokeNet anyway.
Reason 3: It was our fail-safe in case we got shut down by Nintendo
Yeah, sad, but true. We knew it would happen eventually, and wanted that whoever took the project after us kept the project Open Sourced. That’s the beauty of the GPL, it forces derivatives to keep the same license as the original code. Sure, you “own” your modifications, but they still have to be licensed as the original project.
Bonus Reason: We had to.
PokeGlobal / PokeNet was based on ShoddyBattle, a Pokemon Battle Engine. This makes PokeNet a derivative, and therefore, has to abide to the same licensing restrictions as that battle engine.
I hope this illustrates a bit on why we Open Sourced PokeNet. I know I wasn’t one of the devs that chose the license, but I supported the decision and care enough for the project, to continue fighting for it.
On a final note. If you don’t agree with the GPL License, feel free to rewrite the entire project from scratch and choose your own License. 
Oh and if I may give you an advise on using other’s people’s trademarks without permission? Don’t. I learned my lesson, and I strongly advice you that if you wish to use the code, but make your own monsters, moves and sprites.
