Why do some cars get dirty, and some don't?

[smokeydan]

.. or is it the tracks? I've driven my F-Type R Coupe just 20 miles (including a couple of off-track excursions) and it's filthy - unfortunately it was a while ago and I can't remember which track(s)
and then other cars I have driven hundreds (or over a thousand in some cases) of miles, and they are still shiny and new looking...

 

[phil_75]

Car gets dusty at Willow Springs

 

[JacksHerer]

Visible damage being on?
I rubbed paint with a guy in a lobby and there was paint missing from my wing mirror in the post race photo.