At least on Soybooru, it's because being Aryan is seen as good, and Aryans are white, so being white is seen as good. Due to this, every single shitskin from every 3rd world shitskin shithole wants to be white.
Those who wish they were white or more generally western often come from nations that were under the rule of the west in the past. They have no sense of national identity since they have no independent history either, an example of this would be basically the entire South American continent. They are still being colonized in the cultural sense. But for a counter example, you don't see Turks deep throating white people because they have that sense of national identity in question. Plus they never came under white rule. That's how I see this anyway.