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Doesn't really matter why the Wii was successful.
Smartphones/tablets have taken over the market for arcadey/cheap/old-school style gaming. And in the process devalued such a game, no one will pay even $20 for that now that they can get it for $1 and have it in their pocket when ever the itch to play for a few minutes strikes (something else Nintendo can't compete with, most adults simply will never carry a game device with them at all times).
It was revealed recently that females have overtaken the male teenager as the no.1 audience for games, but most of that growth has come from women gaming on smartphones. I see it all the time because I travel a lot ... women playing Candy Crush or something like that on their phones.
Unless Nintendo is willing to sell Animal Crossing for $1 on the iOS/Android marketplace, they are never getting that audience back.
