>3,500 rental cars
Is a tremendous amount of cars. Especially at an airport which everyone has their own active local fire trucks that can be on the scene in minutes and has faster back channels to other fire chiefs in case of emergencies.
Remember what I said, the simplest explanation is due to people being lazy, and lazy is just another form of "greed". The more you know. I would surmise that the execs at the rental company knew that the lock downs would kill their business financially and decided to put the burden on the insurance companies.