Game victory over number 1 Nebraska.
There was very recent precedent that beating #1 in the bowl would get you the #1 spot post bowl season.
UW could have played BYU and hoped to have OU lose to another opponent in its bowl, or just be unimpressive, helping add to the campaign for voters to move UW up to #1.
The mental gymnastics go both ways. Bottom line, UW wanted the sure money of playing in the bigger bowl.
A NC would bring $$$ from merchandise and apparel sales, but there was a risk of not ending up #1 even with a HB win.