"I don't see why more developers don't make more online games for the Cube. Sure, the userbase is small, but Nintendo set up a plan that third parties won't get charged royalties for a game, if they make it an online game. It seems to be a good idea in theory to make online gaming more popular, but it hasn't worked."
From a technology standpoint it makes no sense why the Cube has so few online titles. Activision made Tony Hawk 3 for the PS2 online and that was before the PS2 broadband adapter was even released. Yet they won't make an online Cube Tony Hawk game. From a hardware perspective the Cube setup is identical to the PS2 one: here's a broadband adapter, do whatever you want. However the Cube still has only one online game.
The reason for that is because not only is Nintendo not making their own online game but they're discouraging third parties from doing so as well. It's kind of hard to sell an online game when the console maker themselves is trying to convince the userbase to not be interested in online gaming. Nintendo has sabotaged online gaming on the Cube. Why? I'm not sure. They could have just said "we don't plan on releasing any online games but the broadband adapter is available for anyone to use" but instead they outwardly bash online gaming every chance they get and they haven't made the broadband adapter readily available. It's as if they're such stubborn jerks that they've decided that if they're not going to make online games NO ONE IS. Maybe they don't want a third party online Cube game to be successful because then it means that *gasp* they were wrong all along.