Earlier quoted context omitted.
A 'small' island with one of the most successful and thriving democracies in the East, that has world class industry. China cannot have a successful democracy on their doorstep, it undermines their perception of absolute Chinese superiority.
China is a democracy. It's literally what you're describing Taiwan as. That said I do agree that it does cause China's superiority to be called into question. Imagine if the Confederate states of America managed to take hold of Cuba and hold out. EDIT: I'm literally factually correct. In 5 of the 6 indexes China has a Democracy score where as Brunei, an absolute monarchy, doesn't!
You get to vote sometimes but there's only one party...