Ya it comes down to the fans playing as kids and then wanting new things when they grow up.
Some want a more gritty Zelda (twilight princess will always be my favorite). Some want Nintendo to move in the 21st century and make characters actually talk, crowds like you see in assassins creed, and just things that should make the series move with the times and new technology.
Basically, everybody wants their own thing, and Nintendo cant begin to please everybody.