Let's suppose the chance of a fire is 1% every 10 years. So 100 houses pay 100 * 75$/year * 10 years = 75,000$ per fire. Now if the house is worth < 75,000$ then paying the cost of putting it out is not worth it to the property owner.
As to why it might cost that much per fire, it's probably low probability event so you need to pay for all the time, training, and equipment that sit's unused between emergency's. Add in the overhead in showing up to events like this one where they receive zero compensation and you have a major free rider problem.
Working back from the fee is a very questionable assumption for the cost.
For that matter, I asked whether it was a case of people not reasonably being able to afford the cost five levels up; I'm asking about a "moral" distinction tptacek sees.
As to why it might cost that much per fire, it's probably low probability event so you need to pay for all the time, training, and equipment that sit's unused between emergency's. Add in the overhead in showing up to events like this one where they receive zero compensation and you have a major free rider problem.