I think lvvcsf in post 36 got this right… for high stats kids the net cost of going OOS may be equal to in-state and in many cases, including our own, less.
When we started college shopping, our local high school had a seminar where it was mentioned that IL and NJ send more kids out of state than any other.
Although our youngest applied to and was admitted to UIUC’s most competitive engineering program, the fact that other schools offered so much merit $$ made many of them cheaper to us than our in-state flagship.
Illinois is so broke it plays that game too, trying to fill the class with full-pay internationals and offering merit to strong OOS kids with high stats that will net them more revenue than our own 2400 SAT child who was offered no merit.
Furthermore, here in the midwest, although we do send a lot of kids to elite private schools, the Big 10 schools are very popular as several offer great educations and strong alumni networks in Chicago. I think Michigan and Indiana at minimum equal Illinois’ reputation and alumni network in the Chicago area. Purdue, Wisconsin, and Iowa are also very strong. In private schools, Northwestern and UChicago are local and Notre Dame trumps them both for alumni network in Chicago. With that kind of competition, University of Illinois does not stand out.
All states surrounding Illinois know this and cherry-pick the best Illinois kids. I imagine NJ is the same.
It’s a crazy system when state schools prefer OOS kids to their own.