Because this is the character they had in mind for THEIR game. That's just as bad as saying there are too many (insert any color here) people in a game the developer should change it because I want my character to be (whatever color you wanted) to fit my agenda. And since all the character are modeled off real people my bet is the dev modeled the protagonist off of someone to some extent.
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Also, I'm pretty sure Hana is supposed to be Japanese, not white, since her full name is Japanese (Hana Mizuno) and she originally went to a school in a town called Amaririsu, which is again Japanese. I'm not sure why one would think Hana is white when all of this information makes it pretty clear that she's very likely supposed to be Japanese.