I believe there have been fans in the stands at racing events in the US (including Newton speedway). Is there a reason that is ok for racing but not college football if the same approach was taken?
If you want my opinion, there shouldn't be fans at racing events either.
"Under the guidance of public health officials, medical experts and local, state and federal authorities, INDYCAR and Iowa Speedway will observe safe social distancing and provide enhanced hygiene and safety precautions for all fans in attendance at the event," the release said. "Only a limited number of tickets will be available for the upcoming race weekend, with each group of fans in attendance separated by at least 6 feet of distancing at Iowa Speedway, in order to align with Iowa state COVID-19 guidelines."
compared to this
http://www.storycountyiowa.gov/AgendaCenter/ViewFile/Item/18066?fileID=13807
Health officials are asking for different things from both sporting events.
What you brought up could make the case better that there shouldn't be football period this fall. Racing is an individualized sport involving a pit crew. For the athlete, this is easier to follow social distancing protocols and other necessary measures.
For football, athletes being in close contact with each other and the fact that it's a team sport with 100 people on each side when you account for the staff makes it more of a challenge to following suggestions.
There has been races canceled because of covid in other states. Maybe it's more of a state by state thing? (i'll avoid going deeper into this unless you want this to get political)
https://motorsports.nbcsports.com/2020/06/25/nhra-cancels-seattle-race-due-to-covid-19-restrictions/
https://www.roadandtrack.com/motorsports/a31433138/motorsports-delayed-coronavirus/