Because its incredebly hard and incredebly expensive to do. Being extremly woried about suply chains for geopolitical reason is a thing that came back with Corona and even more so with the russian war against ukraine. Why invest billions into something with no or litle monetary benifit if in the last 30 years nothing has happend that interuped the existing supply chains. On another note its not just sensitive to geopolitcs in SEA and EA its just as depended on Western European and American geopolitics. So if you realy want to become indepened from the rest of the world for chips be ready to invest proably hundred of billions and if nothing happens in Taiwan you gain basicly nothing.