Basically what happened is this -- Nintendo fans used to buy tons of third party games. Then what used to be the Nintendo fan base became split after the N64.
You had one group who loved Mario/Zelda/Metroid/etc. so much that they were willing to stick with the N64 and continue on with the GameCube. This group of fans though was mainly fanatically about Nintendo's core IP, they didn't care much for third party stuff.
The second group of people who grew up with an NES/SNES liked Nintendo franchises, but also loved a wide range of third party support. When that became clouded by the N64, this chunk of fans bailed out on Nintendo for Playstation (primarily).
So the group of Nintendo fans that grew up with an NES/SNES and really loved third party games moved on. What was left was a fanatic core of Nintendo fans that primarily buy only Nintendo, which is basically the same situation we have today, just the Wii caused a temporary influx of casual gamers who have since moved on to smartphones.







