It makes no sense for china to get a blue water navy

Why would china get a blue water navy with aircraft carriers and oversea bases? This makes absolutely no sense. Even next door china has problems like south china sea and taiwan. Chinese defense should focus on next door and not all the way to africa middle east and europe like america. When the going gets tough the tough gets going. Taiwan should understand when push comes to shove and america suffers enough casualties they will leave taiwan just like vietnam and korea. Even in ukraine it is russian and ukrainians fighting not the west. That's why submarines and missiles can strike at american overseas targets but main emphasis is still defending the territories next door.