It was easy for Utah to defend the deep pass since we gave up passing most of the time. We'd run on first and second down, get into a third and long, and Utah knew we needed to complete a longer pass.
When your offense isn't as aggressive, that alone will typically make the defense look much better.
I'm not trying to say that Utah didn't make adjustments or that they weren't successful, just that BYU made them even more effective.