A speculative piece at Kotaku looks at the release cycle of Nintendo games over the past 10 years, pointing out a current lull that's quite similar to the one near the launch of the Gamecube. They suggest this could be because first-party developers are busily working on games for the Wii 2
"The spring of 2002 was the longest Nintendo game drought on record, and has a number of characteristics in common with the season we're entering now. Nintendo has launched a major piece of technology (the 3DS) and is initiating the gradual retirement of a console with a large and reliable installed base. While we entered into this data mining project with the presumption that we could recognize a pattern that presaged a new console release—the Wii 2, obviously—the last time there was a Nintendo game drought this pronounced was after the release of the Gamecube. Still, you can neatly overlay the release history of the Gamecube overtop the current release history of the Wii—they match that closely."