It's called fairweather fans with the emphasis on weather. Just like ISU, KU doesn't have nearly enough hardcore FB fans. When the weather gets bad, they start looking for an excuse not to go or to stay out after half. See ISU vs Mizzou in 2004...division title on the line and ISU could barely top 40k (and that's paid attendance). Real FB schools don't have that problem because for every weeny that can't handle the cold, there are more fans willing to take their spot. Luckily, ISU has made some decent strides in this area in recent years despite the lack of success.
Your absolutely right, Frak. I also remember a game in November against Colorado, not too many years back, on a beautiful November day when my wife and I were able to pretty much pick our seats. I don't recall the year, but it was a pretty darned good McCarney team and the game was an excellent game. Rarely do you see as nice of days in November as that one and I would have thought the place would have been full. We walked up to the stadium, bought tickets, and sat down in a very good seat (not the seats we purchased).
The excuse always seems to be that Iowa has two major schools so it splits the fan base, but come on, how many does Iowa State graduate every May. Many, if not most, of these graduates stay in Iowa, but still it is difficult sometimes to fill a 50,000 seat stadium. During the early 2000s, when Mac had those good teams, you shouldn't have been able to buy an ISU ticket at any price.