811,
Good point. There was a lot of man made "lightening" during those years.
Why, though, would a landlord wish to torch his property to collect the insurance?
Very simple. The cost of escalating property taxes, utilities, and contractors (plumbers, plasterers, HVAC, ect,.) was greater than could be collected in rent. Every thing goes up but the rent. At some point, the landlord says "I'm outta here".
Oddly, the early history of Bronx landlords is a stellar one. They gambled and invested in the early part of the 20th century to build beautiful buildings that provided millions of immigrants a chance to move up on the economic ladder. They made a nice living from these investments, sometimes for generations, and kept their properties nice to live in. I know.
By the mid-60's these traditional landlords were smart enough to have sold out. Those who came after were the ones who exploited the insurance laws and, in many cases, their own people.
Rent Control was repealed in Boston, Philly, Cincinnati, Chicago, etc, after WWII. Housing there boomed.
New York City did not repeal Rent Control (still hasn't.) Any wonder why the Bronx (or Bushwick, etc.) burned, and there was a housing crisis within two generations of WWII?
No incentive to build or maintain property ...guess what happens? Will we ever learn?