While I agree with you, I'm thinking that this is a response common to sensitive government institutions in general. If this lab leak happened in the US, would we suddenly invite CCP (or Russian/N.Korean/Iranian) agents into Fort Detrick to conduct their "investigations"? Which country would actually allow such a thing?

Consider for a moment the propaganda value of being able to say, "we visited their labs and witnessed first-hand their failure to {do some sanitization procedure} correctly! Oh how they clearly don't value human lives!"