The plot was influenced by a true event. Not all the events in the movie probably played out in real life.
So, given that, I think they wanted (for Hollywood's sake) to hire a white lead actor. It's all on terms of money. Maybe they couldn't find a good Asian lead actor.
Besides, having an Asian lead role is a bit obscure unless they're well-known. The role for the lead actor in this plot could be anyone of any race.
BTW, has anyone actually seen this movie? I'm curious to see it.