Buying carriers too expensive! Build islands which like no moving carriers instead!
Some of these atolls they've built up are a ridiculous distance from China - it'd be like Canada building an island off California and declaring the waters there sovereign.
China is in no position to challenge US militarily. For now. Look at them from say 2005 to now. In ten more years - they are building a LOT of pretty decent naval ships, a large submarine force too. They have hundreds of stealthy and very fast missile boats too, that alone could flip close to 1000 high mach SSMs at US/Allied naval forces. Having runways and logistics on all these little islands is a very serious threat, one that is too late to stop now.
How anyone could think that eventual war, or surrender of the Pacific sea lanes/control by the US/Allies isn't going to happen is beyond me. Eventually China will think itself having enough resources and capability to challenge the US Navy/USAF, and then won't back down or just issue "me so angry" press releases. And that day will come sooner than later IMO.