Firefighting is one of those absolutely basic parts of civilization who's importance is obvious to everyone. If people are robbing firefighters then social cohesion is completely dead.
Many of these thefts are related to economic issues but they come and go. Here's the NY Times in 2008 talking about an epidemic of catalytic coverter thefts https://www.nytimes.com/2008/03/29/us/29converters.html
And it could total their car!
People driving used Hondas may find out insurance won't cover, or will want to just total used cars due to the converter being worth more than the paper value of the car, despite a used market valuing the car much higher!
Cost $1,200 to $2,400 to replace and due to the last round of this theft happening, the legal requirements are now stiff. One can't just go get one of these and install anymore. Has to be done in a shop, and there is traceability on everything. Expensive.
Yet the thieves can still somehow trade the metals.