Interesting, I'll have to see if anyone knows the history on it. Why would a fire truck be a flatbed?
Prolly because at some point, someone (with a torch ...) needed a flatbed more than they needed a firetruck.... but a retired firetruck at an auction was all they could afford ...
My firetruck almost became a flatbed that way. But someone else needed a firetanker more than I needed a flatbed so my former truck is still a firetanker.
At work, we have a service truck (parked now in the junk lot) that started out life as an ambulance for our town's rescue squad. They cut the ambulance box off, ducktaped plywood across the back of the cab and slapped a service body on it and voila ... service truck.

John