Generally, its the language and the culture barrier. Hong Kongers are more comfortable conversing in cantonese, and Chinese people, mandarin. English is not their first language and some people just do not bother to try.
Another reason is the cultural barrier, pubbing / drinking / clubbing is not our (yes...I am oriental) favourite past-time. Some individuals embrace western society more readily, but most do not. It's individual preference.
Bottom line is that, there are a ton of orientals at the LSE, and thus they are more comfortable hanging out around with each other. Once nestled in the comfort zone, there is no real incentive to go out and socialize, sad but true. Also, we tend to be obsessed with results (and thus work ridiculous hours), and not surprisingly we tend to do really well. The top economics student, was a Singaporean this year.
To sum up, we're there with one main objective: bring home a First Class Honours degree. (After all, our school fees cost 10 times more then EU students). Everything else, including socializing, becomes secondary.