Those occupied islands can be used to place SAMs. In addition they have an airfield and harbor where, once local air superiority (not even over all of Taiwan, just the strait) is attained, you can start putting cruise missile, artillery and rocket batteries there.Think about the logistics to supply the troops during a time of conflict or wars. One side has to have both air superiority and sea control FIRST to make those occupied islands useful. Other than that, you're just having the first expeditionary force be stuck with dwindling supplies each day as ships and planes has to contend with enemy surface combat ships, ships, and fighters from nearby runways attacking the supply chain. It makes no sense wasting money and lives on a non strategic islands.