According to this article, white women in China are lonely because, one, they get no love from white men:

Another put it a little more bluntly: "I think white girls here are at a disadvantage because a lot of white males here have some degree of yellow fever. There are Western guys that are only into Chinese girls."
Two, white woman are just not into Chinese men:
Some female expats themselves readily admit that they just aren't attracted to Chinese men, much to the dismay of some of those men.An Asian-American told me his woe of being part of an unloved cohort: "The media just doesn't portray us as sex objects. It gets even worse with Western women because the height factor alone is a problem. Women want to date tall guys and a lot of us Asian men are smaller than the white girls."
Of course, none of this is in any way scientific. It's nothing more than a small number of observations made by the reporter and the people she interviewed. Let's leave it at that.