The Chinese have neither the lift capability nor the experience to invade a huge island defended by a million angry Chinese.
Meanwhile the million natives of Formosa/Taiwan wish all the Chinese would leave. When it was a territory of Japan, the Japanese classified and identified all the tribes and groups of Taiwan (classed as subgroups of Austronesians). When the nationalist Chinese invaded following WWII, the natives were repressed and the Chinese ruined many benefits given to the natives by the Japanese.
When the Chinese go into another land, they completely take over the land for Chinese. The Austronesians are now a small minority in their own land (perhaps 5%).