Iowa can be solvent simply by putting a Cup race there. That alone changes the economics enough to make the place worthwhile. The issue NASCAR has is that their Cup sponsors by and large don't care if they are in Iowa. Not enough people living there, the people who live there have a lower-than-national-median household and per capita income, they lag behind the national averages for broadband access and internet use, they have a larger population of elderly than the national average, etc etc etc.
In a slightly different business model, Iowa is a place that could totally be sustained by running Truck/Xfinity/Indycar, but NASCAR has moved away from that and is principally interested these days in media rights. That would seem to be a benefit to Iowa conceptually since it means tracks can be solvent and sustainable without selling a single ticket to a fan, but there are consequences to that also in terms of what TV partners and advertisers are seeking.