Why do major LLMs block china? Isn't that a potentially huge market for them?

Early on there was a lot of distillation going on, apparently. Note that OpenAI introduced ID verification for high volume accounts and I think it was for that reason. It does raise questions about how much of the Chinese model's performance is entirely home grown. At least historically, it was quite hard to crawl the English web from behind the Great Firewall.

I'm not sure, but my guess is that it's due to pressure (or perceived pressure) from the U.S. government.