The divide is largely due to the fact the Chinese government has regulations about the quality and kind of social media content platforms are allowed to distribute, including emphasizing educational content for kids etc. Possibly other nefarious reasons you allude to, but those content standard regulations are sufficient enough to explain why Chinese content is segregated - they literally can’t share the same content selection inside China, so otherwise would have to conform to Chinese regulations outside China as well. Those regulations would make TikTok much less profitable outside China, and they’re not required to do absolutely anything to “improve” the content quality outside China, so they naturally optimize towards engagement and stickiness. That incentive is shared by all social media companies, and is why the Chinese regulations exist to begin with - because what’s engaging and sticky is likely really the absolute worst crap ever.