There are many variables to attracting kids both in-state and OOS to a college. Some formulas are clear and some aren’t.
For example, the population of Oklahoma is about 4M and the population of Alabama is 4.9M. Similar states. My D19 had a COA at AL for ~$19K and at OK for ~$27-28K. AL has a larger enrollment by about 6-7K. Exactly why AL was cheaper than OK I am not sure. Either way both were cheaper than UIUC.
But @Knowsstuff is correct the high stats kids leave IL. You can get a better deal at many places. The mid-stats kids stay and some high stats kids still go there for eng. The word does travel from kid to kid quick and UIUC get bad mouthed like crazy for no money.
I would love to see a break down of kids with a 33+ or equal SAT and see which states are net importers and which are net exporters of those kids.