I see the main reason is that it's a core tenant to Xi's current CCP that there will be one China and they want to destroy them. The existence of a Chinese demo

I see the main reason is that it's a core tenant to Xi's current CCP that there will be one China and they want to destroy them. The existence of a Chinese democracy is intolerable to them. It certainly goes against the stated vision that the communist China state will be the most powerful country in the world, lead all the Chinese people, etc. Just like Honk Kong was an intolerable example of (basically) free and democratic thinking.