So if you're China, and you think you're going to have to go to war with the US, you might reason that you can fight that war over Taiwan or over the Philippines. Fight over Taiwan and you alienate the Taiwanese forever; fight over the Philippines, and you might even get Taiwan on-side since they claim the 9-dash line as well. And you deplete the US's resources either way. Once the war for the SCS is over, Taiwan might approach the question of reunification differently...