The university of Illinois is hard to get into because they cap enrollment and they rely upon Iowa and Iowa State to educate the kids that can't get into Illinois.
We get out of state tuition and the Illinois government doesn't have to expand any of the illinois-based universities.
You generally have to be in the top 10% of your class to get into Illinois. Imagine being in a suburban Chicagoland school that has 500 kids in a class and you're the 70th rated kid and can't get into Illinois. Iowa and Iowa State welcome them with open arms.
Wisconsin has similar situation with U of W.
Isn't that why God invented Western Illinois?