The research out of this lab didn't help develop the vaccine, so what were they doing in the first place? Weapons research, it's as simple as that. As soon as the virus started circulating through the public, that was their chance to shine! They could have released everything they knew and jump-started vaccine development.. but they didn't. They covered it up, because fighting bugs was never their interest in the first place.
Why should anybody believe otherwise? Principle of charity? Please.
Even if I were to accept the (ridiculous) premise, it's still wrong.
Wuhan Institute of Virology did actively contribute to the development of the Vero vaccine by Sinopharm.
Regarding the premise, there's no reason to believe that a lab working on coronaviruses (quite common) that did not happen to contribute directly to a successful vaccine development effort (profoundly uncommon) was necessarily working on a bioweapon.
FWIW, there are ~59 operational BSL-4 labs in the world, and only a BSL-3 is necessary to work on potentially airborne diseases like coronaviruses. According to this study[1] of published research papers, there are probably about 150 BSL-3 labs in the United States alone. Are those all bioweapon programs because they didn't contribute to the vax development programs?
Why should anybody believe otherwise? Principle of charity? Please.