That question is discussed in the article.

“Retaining the best workers is especially crucial in an area like photolithography, where a huge amount of tacit knowledge is used to assemble its machines. An ASML engineer once told He Rongming, the founder of Shanghai Micro Electronics Equipment, one of China’s top ASML competitors, that the company wouldn’t be able to replicate ASML’s products even if it had the blueprints. He suggested that ASML’s products reflected ‘decades, if not centuries’ of knowledge and experience. ASML’s Chinese competitors have systematically attempted to hire former ASML engineers, and there is at least one documented case of a former ASML employee unlawfully handing over proprietary information. But none of this appears to have narrowed the gap.”