One reason of what I assume are many that you're not a D1 football coach.
As Clark posted last night, folks who study this situation statistically suggest that going for it is the better play in that situation. Kicking the FG is the conventional, conservative play. Unfortunately, conservative FB hasn't usually been kind to ISU in the past.
UT's defense is not good (ISU's really isn't either if you look at current rankings). IMO, ISU had a clear advantage when the offense was on the field. Yet, when the game came down to one play that could have sealed an ISU victory, ISU chose not to use that advantage, and settled for a FG. It was safe choice, but guaranteed that UT's best unit would have a chance to win the game, and it increased the opportunity for something like botched officiating to play a role in determining the outcome of the game.
UT is loaded with top talent to play offensive-oriented Big 12 FB. Granted, they aren't coached very well, but they still have the talent. 3 minutes and 40 seconds is an eternity as far as an offensive score in the Big 12. I think the call to kick the FG played right out of ISU strength and right into UT's strength.
In the bigger picture, 30 points is not going to win many Big 12 FB games. The offense was better, but a red zone 2nd and 1 at the 4 yd line has to end in a TD in the Big 12.