In the case of Taiwan, because there's not really a path to victory from straight up invasion that accomplishes anything really meaningful, unless Xi is down for his legacy to be 5 million deaths and the sudden burden of tens of millions of infrastructureless refugees that are apparently full throated PRC citizens now.
The PRC's only realistic hope is a soft power takeover which it seems mildly competent at progressing on. About to have a serious setback with the KMT recalls though.