Because foreigners have just as distorted and idealized an idea of American men as American men have of Asian women?
Try again, it's not just Asian women. It's common in Russia and Eastern Europe for women there to also desire American men. American women are increasingly making demands that make them less desirable to American men, at the same time that foreign women are finding American men more desirable. There is not an equally reciprocal trend for American women and foreign men.
Many of the women who make up 57% of current college enrollment are either going to have to change their expectations about marrrying up educationally and economically, or they will be spinsters as American men take more reasonable options.