I can't imagine what the fan support would look like at ISU if we had some success like Baylor has had.
ISU would show up bigger in terms of local butts in seats, no question. However BU does really well considering the following numbers:
Undergrad Enrollment: 12,500
Alumni living in McLennan County or an adjacent County: 25,800 (That is around 25% of Baylor's alumni in-state.)
Combined number of local likely attendees with a deep connection to the school: 38,327
So 38,327 for what was a 50,000 seat stadium and is now a 45,000 seat stadium.
ISU by the same measure:
Undergrads:25,500
Alumni in Story County or adjacent county: 45,700
Combined local likely attendees: 71,200
That is 16,000 more than Jack Trice Stadium can hold right now and 10k more than it will after the South EZ expansion.
When half the alumni of your school that live in-state (91,000) live within 1 county of ISU it's going to show strong turnout. That is simply a LOT of people that would have a strong connection to the program and don't have to travel far to show it. You would expect to get a lot of these people to show up.
So Baylor will rely much more than ISU does on out of town alumni or casual fans with no historical connection to the program to fill the venue.
So ISU would likely draw more people to the stadium but due to demographics and geography it isn't a knock on BU. Simply mobilizing more people who either aren't historically tied to the school or have to travel long distances isn't going to happen as easily. ISU does a great job with support and gameday culture but having that many alumni nearby is a big advantage.
The school that should be embarrassed is KU who has 146,000 combined undergrads or nearby alumni and can't fill their stadium other than their 2007 season with 3x the number of people needed to fill it nearby.
Other schools combined undergrads and nearby alumni totals:
KU- 146,00 (50,000 stadium capacity)
KSU- 39,700 (50,000 stadium capacity)
Mizzou- 48,000 (60,000 stadium capacity)
A&M- 63,000 (90,000 stadium capacity)
TCU- 33,500 (45,000 stadium capacity)
WVU- 40,588 (63,000 stadium capacity)
GT- 49,292 (55,000 stadium capacity)
Rice- 18,396 (47,000 stadium capacity)
SMU- 46,000 (32,000 stadium capacity)
Houston- 182,700 (40,000 stadium capacity)