FDIs stay in HK in order to enter mainland China. China does need FDI but China does not relay on FDI as a country implemented planed economy.

FDI stay in HK because the LAWS in HK are more fair, and the court system is not a farting joke.

China gets $100 Billion+ annually in foreign investment. 70+% of it from Hong Kong. I don't think any CCP officials would laugh at a significant drop in that figure.

FDI goes through HK only because Chinese government says so. Many ppl invest in HK because of its low taxes.

Low taxes, yes. But why don't these companies/individuals just choose the special economic zones in Shenzhen and Shanghai? I'll tell you why: The court system. Hong Kong courts are based on British-Law and are much more fair and justice-oriented. The Chinese courts are based on how hard the judge wants to suck the politburo's dick at any given time.