They are running down the Taiwanese air force. Every time China violates their airspace, they have to scramble interceptors to chase them off. These then need to be maintained, fueled, parts replaced, pilots rested, etc. If they don't intercept, China gets free reign in the air to scout out their terrain/emplacements/etc. If they turn on the air defense system or more tracking systems, China gets to find out where they are for later. China can afford to it, since both they and Taiwan know that Taiwan can't hold for long if they actually response to these acts of war with war.

Honestly, might be best to put full coverage dead man switch bombs around the country and tell China they can have Taiwan when the radioactivity dies down.