As a society, we cannot ignore the cost of the "Act of God" level disasters when summing up the cost of said disaster. If an insurance companies might be able to avoid paying out on a claim doesn't mean property (or lives) did not get lost.
In my mind the issue is pretty simple: if you buy a house in a wild-fire prone area, you should expect a wildfire at some point. Whether or not you want to prepare by a) purchasing insurance or b) wild-fire proofing your house is your prerogative. If you're not willing to take/mitigate the risk, then live somewhere else.
Or changing conditions throw off their actuarial tables, making the company insolvent when reality intercedes. Those changes could be as obvious (at this stage) as climate change, or as subtle as a long-standing practice of preventing forest fires, which while seemingly preventing property loss to fire is actually creating an unstable system which has the capability for much larger destruction than the typical fire.
Life insurance spreads out risk over a large span of time for the same person. Life insurers have to be more careful. They have to invest the premiums wisely, so that they will have exactly enough cash on hand to pay out the amount of the policy on the expected date it comes due (along with some profit). If the person dies earlier than expected, they could lose money. If the person dies later, they could get more profit. Furthermore, if the investment market is unexpectedly good or bad, that affects the insurer's ability to pay the benefit. Life insurers can rely on the fact that while all people eventually die, they don't all croak at once. There's actually a predictable rate, so if you get enough people to buy policies, you're never paying out more than you take in.
Disaster insurance is more like life insurance, but even harder to pull off, because all those benefits are probably going to be paid at exactly the same time. So what insurers have to do is take that gigantic, elephant-choking payout and let each underwriter take a little bite of it, until it's all accounted for. They're spreading the risk over multiple people, long periods of time, and multiple investors. And even so, thanks to the fact that it is essentially an enforced savings scheme, a big enough disaster would be a shock to the financial markets.
But there's no way around that. If a storm destroys one of your windows, you're going to be buying a new window, instead of some other thing that you may have wanted more. If it destroys your whole town, a lot of money is going to shift from savings and investments into construction.
There is some advantage to having disaster insurance. First off, ordinary people are absolutely horrible at reasonably judging risks. Second, we are also pretty bad at compartmentalizing our savings and investments. If you have a 100-Year Flood fund, and a Yellowstone Goes Kablooie fund, and a Bad Tornado Season fund, and your grocery budget stands at $20 for this month, would you have the fortitude to eat nothing but beans and rice for four weeks? And third, institutional investors manage money better than a lot of individuals, and can take better advantage of the tax laws. It isn't hard to just dump everything into the Fideliguard Some of Everything Index Fund, but some people still put all their money in an ordinary commercial bank savings account, where the interest doesn't even cover the monthly service fees, but it still gets taxed.
But as you say, a lot of those advantages can disappear to just one bad actor in the insurance company trying to cheat a little for some personal gain. The best thing people can do to manage disasters is to be aware of their own risks, and to plan ahead only for those scenarios that have a reasonable likelihood of occurring.
That's a weird definition for "natural" you're using. I think you mean something more like "typical". Unless you're making a theological point, an "act of God" is quite literally as natural (in the sense of un-artificial) as you can get.
But the grandparent's point was economic. Disaster insurance can't work: the whole idea behind insurance is that "bad stuff" happens rarely to some people, so everyone pools money together to pay for the few who actually needed. Disasters happen broadly, and to everyone who needs it in the affected area. A "correct" insurance scheme there would be tantamount to everyone having to just save money on their own, there's no efficiency. And of course in practice the insurance companies cheat and don't save enough, so people don't actually get paid.