Japan Wii owners are just casual gamers that want MARIO and only MARIO. They do not like other good games.
Advertising is also another issue. If you spend so much money on making a quality game, then why not spend a bit more to advertise it.
Marvelous and Xseed games are amazing pubs that make extremely outstanding games but do not sell outstandingly well such as No More Heroes 2: Desperate Struggle and Little King's Story which are perfect examples.