It's because they don't dare say they have a negative view.Imo the reason for their answer is precisely development, since Asian Americans responding with don't know for those countries is basically saying that they're poor countries that aren't as wealthy or cool as Korea and Japan, but the American media doesn't portray them as enemies so, "no opinion, but awesome food btw."
As for the diaspora, simply put since American coverage of their nations is rather favorable as "allies" against China, they feel more comfortable saying they have favorable views of their native land.