Could someone please help me understand why chip manufacturing is so hard? Like why hasn't China already figured out how to do it? It's obviously a huge strateg

Could someone please help me understand why chip manufacturing is so hard? Like why hasn't China already figured out how to do it? It's obviously a huge strategic priority for them, yet it seems like they don't have the requisite expertise to do it themselves. Other bleeding edge tech they are fully on top of (the software side of AI for example). Why is that?