I can answer that.
Kirk was forced to become "New Kirk" after the 2014 season and became far more aggressive. They started going for it a lot more on 4th down, opted to go for a TD instead of FG, were willing to run a bunch of trick plays on special teams and in general played with much more abandon.
It worked and the program also rose to another level in that time, but it feels like the last 2 years Iowa has slowly reverted back to the previous ultra conservative "Old Kirk". This year they opt to settle for a FG even before the drive starts. If they do run a trick play, like they finally did yesterday, it is usually half assed.
My guess is because of all of the success, Kirk feels a lot more comfortable just going back to what he is comfortable with, and that is playing a brand of ultra conservative football that he adores deep down.