If looking at a different angle from that of "putting political pressure on Taiwan by flying into it's AIDZ", and viewing this as the designated flight training zone over open water would make more sense.
Rather than intrusions on Taiwan's rediculous ADIZ (coverage wise), they are just doing year long regular/routine exercises in an area just off Mainland China's coast.
Though IMO much of the exercises could be related to preparation for a war if Taiwan declare independence from Republic of China. If the last remaining ROC province cease to exist, PRC will act to recover the island province to uphold intergrity of Greater China (which is Mainland China, Hongkong, Macao and Taiwan),