My 2 cents here, I think it has to do with location and during the week. That is my excuse. Lets face it, ISU is in the center of the state, a 2-3 hour drive will get you there from most of the bigger cities. Iowa City is pretty far for a drive on a week night for the western side of the state. Des Moines metro is closer or a 30 minute drive to Ames than Iowa City is at about 1 and a half hours. Boone, Jefferson, Fort Dodge, Carroll all within good driving distance. Easy to get off work at 5 and still get to the game. Des Moines you can not do that for a 6 game to get to IC. And even the eastern population has about a 2 hr or less drive to get to Ames. Sioux City and CB locations are not terribly far either, maybe 3 hours.
I also think some of it has to do with losing by 30 to them earlier in the year, and the thread of another Fran collapse that no one wants to be a part of again.
I live 2ish hours from Ames, but 4ish hours from IC.
It is also about 1200 bigger than Hilton and not as good as an atmosphere. Free tickets or not. The students need to go to games but are stuffed in the corner away from the court. I know those are excuses, but I am trying to rationalize it. I can not go to the game due to other obligations. I will have to miss it on TV too.