EA says Nintendo is responsible for two thirds of Wii software sales, which makes creating successful third party games a bit tough
“For those of us making console games, that’s a challenge that we certainly have to contend with. …but there’s no question that having the lead platform be a platform with two thirds of the unit sales occurring to the first-party owner is a really unusual thing. We haven’t seen that since prior to the [original] PlayStation. We’ve got work to do on the Wii.” - EA CEO John Riccitiello
EA has had some successful titles on the Wii. I think they are finding out that it takes a lot of development time and research to find how to create titles that appeal to the Wii-owning public.