Cedar Rapids sits in a cold, moderate climate band, and the freeze-thaw cycle through the winter months is hard on steel panels that already have a weak point - a prior dent, a rust spot, a loose hinge. Steel contracts in the cold, and a panel that's already stressed from an impact is more likely to crack along that stress line once temperatures drop. That's different from damage that just happens from a backed-up car; it's damage that gets worse because of what the season does to metal that's already compromised.
The other driver is simply the age of the housing stock. With most homes in the area built in the 1960s and 70s and the overall range running from 1943 to 2011, a lot of doors out there are originals or first replacements, meaning the steel gauge and panel profile are older designs. Older steel dents and tears more easily than current panels, and once one panel on an aging door starts to go, the rest of the door - same age, same wear - usually isn't far behind.