Mortenson & Westwind ... many of the students at IL State are highly qualified students who didn't make it into the U of I for a variety of reasons.
In fact, the U of I and ISU are considered as the 2 schools of choice - for many state residents - in the State of Illinois. Most other "regional" state schools (e.g., SIU, WIU, EIU, / NIU not so much) have wrestled with declining enrollments from the hey-days of the 1980-2020 period. Only the U of I and ISU experienced minimal effects on enrollment numbers. In spite of increased demand, ISU capped enrollment at around 18500 because of - largely - geography (Watterson Towers - the worlds largest undergraduate dorm). A smaller, more personalized campus with the benefits of a large university. SIU Carbondale is a great example... in 1991 it boasted almost 25,000 students; yet, by 2016 (25 years later) the total enrollment had fallen to less than 16,000 students. Illinois State University and University of Illinois both reported record-high freshman enrollments in 2016. For WIU, the highest year enrollment was in 1973 when they enjoyed almost 15,500 students on campus. Their fall 2024 enrollment was less than 8000 students. A variety of factors influence these numbers including, for example, changing demographics (fewer high school graduates), transportation costs (400+ miles from Chicago to Carbondale), increased competition (U of I Springfield and Bradley/ISU probably hurt WIU's recruiting efforts in Springfield and Peoria. An interesting aspect of WIU - in the context of international students discussed above - is the fact that 58% of their students report white as their race while less than 2% report as Asians.
The big question for potential applicants, and their parents concerns the quality of an education from one of these schools. The best rule of thumb is to go to the best school where you get accepted as a student.
U S News & World Report ranking results ...
School Ranking ... as a National University ... U of I / 33 ... ISU / 220 ... NIU / 273 ... SIU / 288 ... WIU / ranked as a regional univ midwest 38
School rank as a top public school ... U of I / 9 ... ISU / 119 ... NIU / 153 ... SIU / 155 ... EIU ranked as a regional university midwest / 54
Mort & West ... I'd say you made good choices!