Don't be baffled - do the sums!
Even assuming an insurer could be found that was prepared to quote for the sky-high cover you suggest, the company's profits need to be large enough to pay the premiums.
I think you'll find that starting from where we are (insuring against a risk - ie. volcanic activity combined with particular weather conditions -with unknown probability but proven consequences costing billions) there's no way now that this risk could ever be covered. Far too open-ended. Insurance companies are not charities: they're in business only to make money.