International students love it and many would not go elsewhere.
Where is the evidence for this? I have met enough international students to know that it can be really tough to be uprooted at 18, find yourself in the centre of a large city, on a tough course, perhaps in a different language. Culturally the British students may be different, seeing freshers week and beyond as a time to party. The international student could well be being financed by the extended family and see it as their duty to work hard.
London is easier. There are plenty of international restaurants and other cultural facilities. The Universities tend to stay open over Christmas and Easter (important, even places like Cambridge empty out potentially leaving an international student isolated). There will be a critical mass of students with a similar backgrounds.
I recognise that your DD shared a room with an international student and apparently did not enjoy the experience, but anecdote does not make data. However I think you are not taking into account how diverse international students are. "The Chinese" can be Singaporeans with English educated parents, they can be kids who went to international school in a non Chinese country, they can be the children of take away owners in Wales, they can have been through an English boarding school. (DS had friends in all these groups.) There will be some from very rich families in China, who are using time in the UK as a form of finishing school, and who may be congregated on certain courses. But that is a University issue. There would be similar complaints if a course were full of Tim-nice-but-dim's who chose only to mix with each other.
DD was friendly with a group of students from various European countries. The international students chose to share a house together in their second year. They were quite a diverse group of characters but what they probably had in common was a need to hold back from full immersion into a British student culture they did not fully understand. It is a choice often made by, say, British MFL students taking a year abroad who then find their friendship group is from all over.