I don`t know - i don`t think anyone outside Nintendo knows - what happened for Nintendo to lose so much presence in the west.
Whatever happened, the truth is Nintendo never allowed NOA or itself, to replace the missing studios or deals and that has hurt them.
During the N64 (mainly) and GC days, despite having sports games from 3rd parties, Nintendo still invested in it`s own sports games. Why? Because those were the titles that people really wanted. And Nintendo strived to give them those games.
Nowdays, people want other genres (shooters, open world games, cinematic adventures, etc.) and Nintendo has no studios to, not just make games, but to create brands. So, they resort to buying games/brands: Lego City U, Bayonetta 2, Devil`s Third, W101.
Problem is, Nintendo doesn`t own the studio, nor the brand. Anyone can come in after a successful game and just acquire the studio or just that brand and there goes another game away from Nintendo.
Problem is, and you are right about this, Soundwave, most of these games come from Japan - and they show exactly that.
If Nintendo can`t make deals to have western studios make exclusives or crossovers for them, then it`s time to either buy a studio or build a few of them to have games tailored for western audiences and help fill the gaps of games Nintendo can`t create.
