Is there a language issue? (I assume all the top journals are international and English, but are there also Chinese language journals which are influential in China but not considered "top" globally?)

If you have top quality work, where are you going to publish it?

If you have quality work and a big enough local market for it, where are you going to publish?

It's kind of like comparing the %-age of American versus Chinese actors who work in Hollywood versus the Chinese film industry.

Some material might also be most relevant within China, or where the users are Chinese language primarily, so it would make more sense to publish locally -- Chinese history, current politics, maybe some specific economic articles around China, potentially things related to major Chinese engineering works like the new space program, etc.

(Still no idea if language is even a factor, but it seems plausible.)