Not sure if you are looking for some deep explanation. I can't tell based on the question. Anyway, animal crossing for the game cube has (had?) collectible items such as NES games, though they could only be played if you also had a console item. Basically, you could play NES games in animal crossing. The post seems to be mainly about hacking this part of the game to allow playing other games. As to why it has the ability? Idk? Because developers decided to include NES emulator as part of the ROM.