Anti-Asian racial slurs going unchallenged. Unfortunately, not all non-Asians recognize the offensiveness of these terms. Asian arts as negative when practiced by Asians but positive when practiced by whites. On TV, an Asian who knows martial arts is likely to be a villain, while a white person who knows martial arts is probably the star of the show. Culturally distinct Asian skills positively and realistically employed by Asian people.
White actors have disproportionately more opportunities in the industry than Asian actors do.
So, whenever a white actor is cast in a lead Asian role, this perpetuates a racial double standard and diminishes already scarce opportunities for Asian American actors. And just because a part isn't explicitly written as Asian doesn't necessarily mean that it can't be cast with an Asian actor.