Nintendo believes it's Japanese audience is older and more sophisitcated, and it believes its Western audience is younger and less mature, and has parents looking of their kids shoulders. Hence they change their product for what they perceive is the mainstay of their western audience.
Either that, or they want to maintain an image of being the family console in the west and thus they try to stay below a moral line with western games.
Either way it's Nintendo making decisions for its own reasons and if they think it's good for business then they are hardly likely to change.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix
