That depends on what you mean with "pull out". Typically you pay a premium and that means you are insured for a certain period. A year or so.

Everybody who is insured at the moment of course needs to be paid by the insurance under the terms they had agreed to. The insurances should not be allowed to "pull out" of this responsibility.

But what about the next year? If no insurance wants to offer you another term, especially not for those same conditions, then it's their choice to "pull out" in that sense.

On the other hand, suddenly not offering cover at all is a problem for people who have established interests in a property.

I can see an argument for not writing new policies in an area. But I can also make an argument for allowing existing policyholders to renew -- maybe not at the previous rate, but at an appropriate rate for the risk.

As a matter of public policy, we ought to match the risk put on a homeowner with a mortgage by the bank with the risk assumed by the insurer when the homeowner pays their policies. Not let the insurance company lay the risk on the homeowner if they notice the risk has gone up before the loss is realised.

Alternatively, we need to start treating buildings insurance more like (UK) life cover: I took out decreasing life insurance when I took out my mortgage, it'll pay off the mortgage if I die. The amount of cover goes down every year to roughly match me paying off my mortgage. No matter what happens to my health in the meantime, if I keep paying the premiums then I keep the cover -- even if I wouldn't qualify for new cover.

Or maybe we need to say that if an insurance company declines to renew because they think the risk has risen too much, the customer should be allowed to claim on the expiring policy even if the house is still standing, because it's obviously worthless, and it's obviously due to a risk that was covered by the policy.