Something is only worth what someone will pay at any given point in time. A 30-year mortgage assumes the house will retain at least its original utility for 30 years.

Whatever a house is worth today matters not if it's flooded tomorrow ;)

So yes, or course, you're right, inflation hits everything. But the point of the story is that a growing group of homes are no longer insured, and for others, the insurances is growing FASTER than the value of the house (more than 3 to 1, as in your $100K to $300K example).