Economically HK isn't that big of a deal compared to the rest of China at this point.
In CN there are largely three types of listings A shares, B shares and H shares. A & B are listed on SZ and SH exchange and are not freely traded like you know it from the west. H shares are listed on HK exchange and are freely traded using the Hong Kong Dollar.
This is why companies like Tencent are dual listed on Shanghai and Hong Kong exchange, to facilitate foreign investment that wouldnt be possible in the same way if Tencent was only listed as B class on Shanghai exchange.
> But the Hong Kong government can only welcome the stock listing opportunity to reinforce Hong Kong as the world’s premier IPO destination, especially at a time when the introduction of the national security law has raised concerns about maintaining the city as a global financial hub.
[1]: https://www.scmp.com/comment/opinion/article/3145952/why-chi...
The US’s capital markets support international trade in a somewhat similar way, and are thus innately valuable even without accounting for the productivity of American workers.
https://www.reuters.com/article/us-hongkong-protests-finance...
We should also note that with the growth of Shenzhen and other mega cities, HK isn't that important to China anymore. That's part of why they've become more aggressive in the situation.