The casting reeks of Hollywood executive shennanigans. I hear Nintendo tends to be extremely picky and hands on when it comes to adapting this stuff. Mario was supposed to appear in the Wreck it Ralph movies, but Disney couldnt reach an agreement with Nintendo on how to portray him, so they left and went with Illumination instead, which makes me think that they gave Nintendo a better deal, a bigger cut, more creative control, something like that, I dont know.
Maybe they just convinced Nintendo that having a big "Hollywood Cast" would be great for the movie and for its box office. Shigeru seemed pretty hyped about "the talent" involved. At least they're giving Charles some cameos.