Think the Universities "business" plan is to create a "bubble" around its students, faculty, and staff in order to accomplish its primary mission; creating leaders, scientists, engineers and scholars for the state, nation, and world. We see testing, staggered arrivals, quarantine, no breaks, etc. to further that goal. Playing football violates that effort on every home game Saturday.
Arguments can be made for "no fans" but you still violate the spirit of the policy, as well as create institutional problems.
1. Visiting teams, and all their support staff are invited to campus.
2. While I realize this would not happen at ISU, well maybe, programs would have to deny admission to those big corporations and fans who pay for suites etc. admission. Yes they are isolated, but they have to have hosts, security etc.; again violating the bubble concept. If that big oilman from Texas can't get to his seat in Darryl Royal stadium, or that insurance exec pulling his weight in Columbus trying to access the "shoe" is a PR nightmare and potentially can have a large impact on future support for the institution.
3. A lot of college football is surrounded by Alumni activity, and is one of the strengths of the sport. Denying access to some and not others could impact alumni relations for years. Think of the negative PR when we dropped Baseball and men's swimming.
Those presidents have tough decisions. Guess that's why they get paid the big bucks. But I don't think they will bend to political pressure or other outside influence, other than what the science says they should do, including evaluating all risk factors; including any additional risk to their "business" plan and long term institutional integrity.