You're talking about the Rose Bowl. That is one bowl that has a true brand to it. Here are the ratings for the last 5 Rose Bowls that weren't part of the playoffs.
2019 - 8.7 - This is the Oregon game you are talking about
2018 - 8.9
2016 - 8.6
2015 - 7.4 - This is the Iowa v Stanford game that was over before it started.
2013 - 10.2
It doesn't look to me like Oregon makes a huge difference in the ratings. The Rose Bowl just doesn't want Iowa v Christian McCaffery.
That 2015 game was my favorite Rose Bowl ever. We were having Christmas that evening, no living room TV every time I went to the porch to check I kept coming back with a bigger smile.