The simplest reason insurance is becoming more expensive is that home values have been inflated, both by devaluation of the currency in real terms, and by jurisdictions which are underwater inflating home assessments to increase taxes to provide more revenue.
The result is that a home that was worth $20,000 in the 1960s sells for over $500,000 today. Depending on the area, those increases in market value may make a property high risk for the insurer.
It takes higher premiums to cover the risk.
Changing coastal geomorphology due to storm events over the years makes other properties high risk, and inland properties become less insurable as development (paving) renders tracts of land impermeable, increasing runoff downstream of, and in developed areas. That increased runoff changes the calculus of flooding events because less water is absorbed into the soil and more runs into streams faster than it would from vegetated areas, much like rain falling on an area that has burned.
Insurance companies are in the business of making money. One way to look at it is that they are the 'house' in this gamble, and adjust the premiums to cover anticipated losses on a broader scale to make money. If the house doesn't anticipate making money, or loses too much, they quit taking bets. For the insured, it is a bet that your property/person/life will suffer damage or total loss that only pays out if you 'win' the bet (and suffer the loss).
