They wanted her to be like manga.
James Cameron's words from Yahoo News:
“I think Robert and I were both always in utter agreement that she should look like the character in the manga,” Cameron told us. “With
our first trailer that went out, we weren’t quite there yet. And we
got a lot of blowback from the fans. And there was a backlash reaction
The production budget for the film was about $200 million, but that only covers the costs of actually making the movie. That does not include other costs related to the movie, such as advertising budgets and interest paid to whoever funded the film.
For those of you who haven't read the original manga, Alita is an early generation cyborg. This means that her design wasn't as flawless as newer generations (much like comparing today's computers to, say, a Macintosh 128k). It has little to do with 'manga eyes' or any generalization of the standard Japanese manga art style. In the manga, the size of her ...
The movie doesn’t address this directly. I suspect the manga it’s based on does—I’ve heard it is a vastly more detailed world and plot—but I haven’t read it.
Really, a lot of the reason could easily be meta and narrative—Alita participates in motorball because the author/director want her to because it’s and sets up some other narratives later on. Until a ...
According to this article:
In interviews with director Robert Rodriguez, he revealed that the surprise casting is meant to lock in capable actors for big roles in future Alita sequels, which was a lot tougher to pull off than it looks.
Note that the lack of credit might not solely be due to the surprise effect, but also because of a technicality:
Norton makes a lot of cameos vs the number of his actual appearances. Norton in the past has expressed sentimentality to embracing character's "mysteriousness". I believe his cameo this time was to be a dead-ringer for James Cameron and thus went uncredited to add to the illusion.