It's a anomaly that spans beyond just the condition of cars...everything they own is treated as such!
I've met people who were obviously affluent, but everything they owned was dilapitated...from the condition of the vehicles, to the slow erosion of their incredibly customized homes, including abhorrent grooming habits!
I'm not sure what the source of this condition is, but I believe they are just slobs...doesn't matter how much (or little) money is involved, it permeates all aspects of their lives.
I can't criticize though...many that I know have hearts of gold! And that's more important anyway, isn't it?