While I can see your point Metroid Prime 3 is an adventure game as much as a shooter and as such isn't really designed for the type of play that would occur online. Even co-operative play wouldn't work as one of the features the Metroid series is famous for is making it feel like you are entirely alone (which was ruined in Hunters and would be very ruined in co-op).
Thus I think you are wrong, it simply isn't the right type of game for online multiplayer.