When you look at the process of building an accordion, it is much more complex in terms of number of parts than an instrument like a violin, mandolin or guitar, but the actual "craftsmanship" - at least as it relates to sound , as opposed to finish - is more straightforward. No doubt there is artisanal "skill" involved, but it is the kind of skill that I would guess can be learned over the period of a few years, rather than over generations.
What is required is someone overlooking the whole process who is very experienced & discriminating. What Italian master accordion-maker is going to leave Castelfidardo & live in China for a few years in order to bring a Chinese factory up to Italian standards? And who's-a-gonna-breaka-his legs when he shows up back in Italy?
Hohner, because of the scale of their business have obviously already done this. I'm guessing that the volume of potential business for high-end accordions isn't sufficient to persuade someone to abandon their Italian home & traditions & take on the daunting task of setting up shop in China.