From a spectator perspective Milwaukee and Indy Cars are a good fit. The tradition, history and folk lore combined with generally above average racing would seem to be a very good combination. Lack of interest is hard to figure. Hopefully that will go different if Milwaukee ends up back on the schedule.
With that said, the two best Indy car races I've ever witnessed were waged at Chicagoland Speedway. No. 1 being the year Al Jr. and Hornish raced the last 30some laps for the lead side by side at well over 200 MPH with Hornish ending up the winner by just thousandths of a second. A great one also happened several years ago at Texas but the details escape me now. Why oval track venues that provide that high quality racing can't draw big crowds, TV viewership and wider fan interest when some street courses do

is an ongoing mystery.