Every time I read one of these posts, I wonder what the poster expects as an answer. No one except WN management knows the real answer. It is always a matter of allocating limited resources (aircraft, personnel) in the most cost effective way. The answer is surely different in different cases.

I suppose it is always fun to speculate, but I doubt if it is direct fear of competition. After all, WN goes head to head with AS on numerous routes out of both SEA and PDX - to places like GEG, BOI, SLC, RNO, SJC, OAK, LAS, PHX.