I just have to wonder why they chose Ritzville. I don't understand that one.
I assume its because its (A) part way between Ellensburg and Spokane/Couer d'Alene and (B) along the 395 which links I84 and I90 if you were going from Oregon to Spokane/Couer d'Alene.
You could assert that the Seattle to Pullman route is vastly more important than the I84 to Spokane route and I would have no data to argue with you.