history

There was a small window of opportunity where the PLA could have put an end to the KMT since US forces were occupied in Korea, but US forces were approaching the Yalu River. Partly for geopolitical reasons, partly for comradery reasons, Mao chose to intervene on behalf of the Koreans. This, however, meant the KMT was able to consolidate their hold in Taiwan. If you look at the timeline, the PLA was able to liberate a bunch of islands in May 1950, but they entered the Korean War as the PVA in October 1950. With the window of opportunity closed, the PLA could not liberate Taiwan since the 7th Fleet was there to guard Taiwan while the PLA barely had a navy, let alone a navy that was capable of an ambitious amphibious assault.