Why is Schaumberg Airport (06C) in Chicago an uncontrolled field?
Most likely, the airport was formed in the early-mid part of the 20th century as a small country airport outside of the Chicago metro area.  The city grew around it, similar to Compton-Woodley airport in Los Angeles or Cross Keys or Camden Co. in the Philadelphia metro area.  With the introduction of the modern airspace systems for commercial air travel the Class B shelves covered these airports but did not include them.