Because that's literally the land the hypothetical war would have been started to capture? Because the casus belli to their public has been that it's (PRC) Chinese land by historical and cultural right? Because the entire domestic and international point of provoking a Strait war would be to demonstrate China's strength?

It's a pretty bad look if your "winning" looks like "killed millions of people and rendered the land in question uninhabitable for a decade+." (To say nothing of the potential non-Taiwan collateral damage)