It's almost like white is literally different to all those other racial categories.
White is an exclusionary concept. If someone is half black, half asian or half hispanic, then they are typically treated by society as non-white unless they are white-passing, and even then their treatment will change as soon as their family is included in the picture. They are not considered non-black, non-asian or non-hispanic.
It's easy to say that you would consider them half/half, but that's just not what they experience in the world outside this comment thread, so it's meaningless.