they have not done it, because they are not assholes and/or stupid everything has a cost, however small thy will do it when taiwan becomes a credible treat, some USA nuke missiles being deployed china "peaceful reunification" is a real wish, not empty words remember, people do NOT care on the color of who is ruling over them, they wish security and a reasonable freedom At the moment (see how the covid handling is going) I cannot say that there is ANY country that is "democratic", saving maybe some african one, but they have other social issues. So, the people of taiwan, would not see any difference on being "ruled" now or under china umbrella