Marketing issues maybe? Nintendo has managed to turn non-gamers into gamers, now the problem is how to get these people into "core" gaming.
I also believe that there is a need to attract some of the PS3/360 gamers into buying Wii's or more Wii games if they already has the console. Games like the Conduit won't have much success here as well as multi-plat games that is inferior to the HD versions. Games like NMH, MadWorld and Muramasa won't do much either because they are niche and artistic.
In Japan things might change with huge games like MH3 and DQX (and maybe ToG and FFCCCB, but I don't know if those games are big enough). In the west it's harder because MH and DQ isn't that popular outside of Japan. The Wii should need games in the MGS/FF/CoD/Halo calibur, preferable developed by well-known studios. If Bethesda (spelling?) or Bioware released big titles (not some half-assed money-maker) that would be positive.
Of course, Nintendo's own games may be needed to actually attract people and make way for third-parties. NSMB Wii, SMG2, LoZ Wii and Metroid are important core titles that really need to sell. (Metroid might not be as big as Mario and Zelda but as a Metroid fan I have to mention it :p)
If things hasn't changed in lets say a year and a half (maybe a bit less) than it's better luck next gen I guess...
(I'm tired and should be sleeping so if none of this makes any sense than you shouldn't have read it)
