It's just a textbook example of regulatory capture.
OpenAI and Anthropic are in the lead now so it makes sense to 'slow down' and ensure Qwen, DeepSeek etc. aren't given the opportunity to catch up.
It also makes the assumption that China's progress will slow down in lockstep and I don't really see any reason why they would, Regulatory capture in the US would actually be an opportunity for them to catch up further outside the US.
They pretty much already caught up though. I think the real reason is they have hit a plateau where improvements will be minimal. They are using brute force and it has a ceiling.