There were (and still are) multiple “lab leak” theories that are in widespread circulation, ranging from “it is possible that there was accidental infection at a research facility” all the way to “it is a bioweapon”

The scientific community has always discounted the latter.

Also, science is evidence based, and so many scientists are (rightly) hesitant to make conclusions (and to support others conjecture) unless they have some sort of evidence to support it. China knows this, and knows they can avoid bad publicity altogether by limiting the evidence that is released. Scientists are not in a position to make political accusations in the absence of other information. “We don’t have any evidence to support that theory” is perfectly reasonable scientific statement, regardless of the political realities.