Charles Martinet will be stepping back from the voice of Mario and is taking on a brand-new "Mario Ambassador" role at Nintendo

There is a good argument for not casting him, though. Martinet's voice is good for short sound bites and small single sentences at most, which is mostly what's needed for Mario in the games, and that's something he did very well. As far as the games are concerned, his will always be the iconic Mario voice. Applying that to an entire movie's worth of dialogue, though, would have been painful. No Italian I've ever heard actually speak English talks like that. They especially would not have wanted the Martinet voice for having Mario be a Brooklyn native as in the movie.