Hec- just a couple years ago the theme was Rupp, and 2015 is Rupp again. It seems the top brands of popularity are Cat, Polaris, SkiDoo, Yamaha, Scorpion, Rupp, Chapparal, John Deere, then it tapers off quick to all the other brands.
Yes- a motor theme would be nice to see. Kohler power (American motor) would be another nice theme to see. But yes- I'm sure it has something to do with popularity. I'm just glad to see such an event celebrating the unique and individual heritage of this sport. Nowadays, without the sticker on the sled, if they were all the same color, it is hard to identify any brand uniqueness. They all look the same to me. Prior to the 2000's, the brands still had an unique identity. I find it ironic the brands are renaming some models after vintage heritage. The car companies seem to be doing the same thing in the last few years.
Anyway, any attempt to remember where you came from is a good effort. Good rule to live by, I'd say.