University of Illinois has both University of Illinois Champaign-Urbana - which likely has lower pell grants than University of Illinois - Chicago. University of Illinois - Chicago has more commuters than residents, and that is likely where you’d see a lot of pell grants. UIUC is in a very small city surrounded by very rural areas - it’s not a commuter school for the most part
Though this chart shows that University of Illinois has only 22% for Pell Grant (and it also doesn’t distinguish between campuses). Where did you find 55%?