The risk models for potential members would vary wildly. The fee structure would have to account for different levels of risk based on the activity of members. And then what if one member faces a lawsuit that could be an existential threat to that company, how much of a legal defense is the appropriate response? And then who determines the legal strategy (settle vs court)?

This sounds like ransomware insurance. Often you would expect the insurance to help you recover from losses but instead they just pay the ransoms since it's cheaper. Which in-turn makes the insurance holders even more of a juicy target.