Presumably most white dudes in China aren’t staying there forever. They can get white women whenever they want when they go back to wherever they came from. When in Rome, have sex with the people Romans have sex with.
I was once told something I found intersting by a gay man I worked with — he said that men who like Asian women wake up one day in their relationship with a white woman and think “I want something different.” They can’t quite get to what that different they want is — so they go to Asian women.