Like what if the reason that China won't abide any investigations isn't not that they're covering up the lab leak, but that they're covering up a bio weapons program that also takes place at WIV?

Historically, the coverup is worse than the crime. China made the choice to go "we've got this all handled, our response was better than everyone else, look how stupid the US is struggling with this massive outbreak while we have concerts with 10,000 people in them" rather than disclosing they knew full well how bad things were, had the outbreak entirely characterized and were using their prior knowledge for geopolitical advantage.

This came at a time when China was pivoting from "one belt one road" to "wolf warrior" and every strategic partner China has is in the grips of a fatal pandemic that their erstwhile trading partner not only caused, but failed to aid them against in the slightest.

China's best geopolitical move is to go "you can't prove that we knew we made this, we knew it got out, we knew how bad it was and we knew we were condemning millions to death with our nondisclosure" and then be outraged while others argue just how proven those allegations are. It will be isolating, it will be geopolitically damaging and it will stunt the projected international growth of Chinese ambitions, but the magnitude of the catastrophe is such that their path was cemented as soon as the virus jumped an international border.

And giving outsiders access would be like the US giving access to Los Alamos to outsiders?

There was a steady stream of foreigners through Los Alamos through the height of the Cold War. There were more Norwegians in my elementary school than Black kids. Our high school had classes in German, Spanish, Latin and Russian. We had so much foreign exchange that there was a remedial class to get high schoolers through NM's state history exam, the passing of which is a requirement for matriculation (nobody from Germany took a year and a half of NM state history in 7th/8th grade and it showed).