The reason that Seattle runs every single sportsman class is because Division 6 is the only division that gets ONE national event, so this is the only opportunity for many of the sportsman drivers to play on "the big stage".
Breaking the season down by division, it looks like this:
Division 1 - Englishtown, Maple Grove, Richmond
Division 2 - Gainesville, Atlanta, Bristol, Charlotte
Division 3 - St. Louis, Chicago, Norwalk, Indy
Division 4 - Houston, Dallas, Memphis
Division 5 - Topeka, Denver, Brainerd
Division 6 - Seattle
Division 7 - Pomona 1, Phoenix, Las Vegas 1, Sonoma, Las Vegas 2, Pomona 2
Just a little food for thought