Actually that raises an interesting comparison with the Tibetan diaspora that mostly left during around 1950. How many of their descendants growing up in India/US/UK still know how to speak Tibetan?

IMO assimilation isn't a bad thing, rather an indicator of a culture they bring with them which is accustomed to concepts of citizenry (or even more evolved) and the state (confucianism?).

But it doesn't mean they are forgetting about their ancestors struggle or their heritage either.

not because of some special cultural quality

It could easily transcribed as education, no need to imply cultural patronzing.

HK is in a catch-22. Stay where they are and get absorbed into the Mandarin speaking behemoth that's mainland China like Hakka, Wu, and Hokkien speakers once the CCP starts tearing down border and population movement restrictions, or move abroad to a dozen different countries and be absorbed piecemeal into the Anglosphere. The third option would be for 1 million or so HKers to build a new city somewhere where they could be the dominant culture. Unfortunately, Singapore is a very unusual case in world history where Malaysia didn't care about sovereignty over the land Singapore stood on and actually forced them out. Very little chance of that happening a second time.

They're silent. It's not their ex-colony and, very sorry to say it like this, but HK isn't worth angering China over.

Hong Kongers are likely to achieve more for the world - from UK rather than from authoritarian China. The fate of Hong Kong, specifically, is not that important.