Most people grasp the reasonableness standard for running a disease lab: you were negligent if the diseases break containment, because lab standards should be in place to prevent that obvious risk.

Under the wet market scenario, it's not instinctively clear to me what was unreasonable about the practices of the vendors at the market. Does selling bats more likely than not result in spreading disease? Or selling bats in proximity to pangolins? It seems like the vendors were doing the same thing vendors have done for millennia, not doing something unusually or obviously substandard.

Think about it this way: if a French tourist gets a severe toxinfection while eating in a seedy restaurant in some corner of the USA, would the French state, or even the family of the person, sue the US government for failing to enforce health codes / not having good enough health codes? Would you seriously imagine that trial happening and being successful?

Conversely, say the same person got equally badly sick while visiting a friend who works in a US government lab that researches and deals with live viruses. Wouldn't you feel the US government has a higher chance of losing a suit on this?