It’s largely legislative changes that have made insurance unprofitable in those states. Florida’s bad faith law and banning of international reinsurers have both hurt the industry a lot. California has had wildfires for a long time and their frequency hasn’t increased much over time.
I left a more detailed comment elsewhere in this thread if you’re interested.
In Florida the issue has little to do with rising sea levels at the moment. There’s a Bad Faith law that makes the insurance companies responsible for the policyholders legal bills if the decision increases the amount of the settlement. There are a lot of lawyers that take cases and only bill if they win, and if they do win they bill a lot. There is also a lot of insurance fraud in Florida, both of which drove up the legal costs to insurers. Catastrophic events are more impactful to insurers in Florida since Florida has passed a law preventing international reinsurers from being used. So when a hurricane hits rather than having the costs borne by a larger number of insurers across the globe, only US insurers will be spending money on the catastrophe. This has pushed many insurers to insolvency.
In California rate increases could allow insurers to keep up with rising costs. Note that the percent of homes affected by wildfires is only somewhat up over the past roughly 20 years, the real problem is the increase in severity due to rising property values and insurers being unable to raise rates due to Prop 103. Prop 103 allows for public interest groups to have hearings with the DOI and the insurance company to determine if a rate increase of 7% or higher is justified, and the insurance company must pay the legal costs of the public interest group(s). The lawyers who lobbied for this law have set up a public interest group and start hearing whenever an insurer tries to increase rates at 7% or more. Said group tries to drag out the hearings as long as possible, since it’s free money.
Insurance policies are short-term and climate change is going to take longer to really hit. Climate change isn’t why but rather legislative changes. I’ve left a more detailed comment elsewhere in this thread if you’re interested.