I wasn't aware of Japan having a particularly disconnected tech sphere from the West like China does. Where China has its own independent platforms, technologies, separate SOTAs and completely disjointed research (until the recent 5 years where they've really started converging and borrowing from each other).

While Japan has tech companies, most of their research is coming out of their global offices, and they really are global even when based in Japan. Sony aren't publishing papers in Japanese, they're doing so to Western conferences in English.

Whereas China had its own parallel FAANG equivalent tech giants developing their own versions of Amazon, Google, and Facebook's tech supremacy & its constituent ML advances.

All this to say that Japan engaged in the Western economy a lot more, and subsequently its tech companies engaged in the Western pool of talent, science, and communication a lot more. Meanwhile China had its own bubble until very very recently, and thus a lot of the world's unique & innovative ML has been conducted in Mandarin.