I guess I don't quite understand why. If HOU wins, they aren't getting caught for the Big XII title.
Best path to ISU winning Big XII would be AZ win. Would still need help, but if AZ beats HOU...and ISU finds a way to beat both HOU & AZ (would probably need ISU to win out) then ISU would at least have a chance.
If HOU wins today, it'd be really hard for ISU to get back into it without a HOU epic collapse ir injury down the stretch.
If we're rooting for HOU, I'm assuming it's not for Big XII title reasons, maybe just ranking/ncaa tourney seeding reasons?