I didn't realize this was even an assertion that people made at all. It doesn't make a lot of sense to me. People at the time must have known that fires in cities were extremely dangerous because they could spread over a great area. It's logical that insurers would want to work together to prevent all fires, purely out of self-interest to protect their insured properties, and then sue the pants off negligent and/or u…
That's the point though. In spite of the logical and practical evaluation, there was evidence from multiple, trusted sources that said otherwise. And history is full of people doing dumb things and making bad decisions, so why not this one too?
Also, it's self-affirming - "Look at us! We've got problems, but at least we know well enough to fight fires when there is one, despite money problems"