The problem is that in American home-buying, insurance is often compulsory for a purchase with a mortgage. This makes sense from the bank's perspective--they want to insure their collateral. However, the system doesn't really have an answer for "what happens when their collateral becomes uninsurable?" Even though lenders have force-placed insurance, even those insurers can deny coverage in certain circumstances (e.g. flood plain). This puts insurers in a position to de-facto foreclose on not just one person's house, but swaths of houses in regions they (as an industry) deem risky.
I'm not sure what the answer is here other than forcing insurers to insure (which would raise premiums for everyone), or creating meta-insurance of some kind (insurance against becoming uninsured).
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