Iowa has about 40/60 paved/unpaved ratio. Wisconsin has about 85/15. (stats counting only primary and secondary (county) roads).

ref: https://bikeiowa.com/Feature/1543/iowa-gravel-what-makes-it-..., https://www.fhwa.dot.gov/policyinformation/statistics/2008/h..., https://topslab.wisc.edu/research/tsmo/topms/data/

I acknowledge this may not be a 'bad' attribute, it could be Iowa just has so many unpaved extra roads it skews it. But when I think Iowa, I think driving on rough roads.