1.
The system is gamable by the trolls. Hurricanes don't care if you're insured, but trolls have an interest in taking troll insurance down. The way insurance works means that if you have a statistically unlikely run of bad luck, you could topple the whole insurance enterprise and leave those who thought they were covered out in the cold.
If I were a troll, I'd get together with other trolls and coordinate enough legal pressure that it was impossible to go to court on all the pending cases at once.
2.
Having insurance like this legitimizes the whole trolling issue, instead of fixing the systemic issues that cause it in the first place. You might think that doesn't matter since we can't really fix the trolling issue, but we can (maybe) create insurance to route around the problem. But here's why it actually does matter: if the troll insurance works and isn't killed by my point #1, then we've actually created a lobbying group with a vested interest in keeping trolling alive. In other words, the organization we created to protect us, if it actually works, will have strong incentive to work against our long term best interests by allying themselves with the trolls they are supposed to be protecting us against.
We'd essentially be creating a protection racket to extort /ourselves/.
Can't see this working.