iirc it is because it heavily implicates both Peter Daszak, who was the head of the UN investigation of the Lab Leak theory, who orchestrated the Lancet letter denouncing the Lab Leak theory, who has now been shown to have conducted gain of function research on bat coronaviruses at the WIV, and Fauci who provided funding for this through Daszak's EcoHeath Alliance and NHAID after there was some sort of restriction on that kind of research stateside. On top of that China is completely uncooperative with the effort and wouldn't provide any evidence to implicate themselves.