Simply put.....
.....there is nothing to "get" about a rrat rod, nor any other persons cars. It is theirs and theirs alone.
I too at one point did not get the large amount of late model cars entered in car shows. Corvettes, Camaros, Mustangs, Challengers and the like.
Nor did I get those big wheeled cars.
Then I started talking to the owners and soon after I did indeed 'get it'.
They love cars as much as anyone else they just look at them a little differently.
Take a look at your wife, and your freinds wife. Are they the same? Chances are they are not.
Do you have the same dog as your neighbor?
Your house the same color?
I get rat rods, and their owners/constructors.
Art is truelly in the eye of the beholder. There is nothing to get.