The GOP party could of nominated winners, moderate Corrine Wood lost to Jim Ryan, 2006 Jim Oberwise lost to JB Topinka, 2014 Kirk Dillard lost to Bruce Rauner. The GOP primary voters are so far right, they nominate the ones that are less electable.
Oberweis is quite a bit to the right of Topinka. Of the 4 candidates in 2006 the GOP nominated the most moderate of the choices by anyone's measure. Ryan was the middle candidate in terms of ideology of the three that ran in 2002, and was a popular AG.
In consecutive elections the GOP nominated a popular center-right statewide office holder, a very moderate (some would say liberal) statewide office holder, and a conservative long-time state senator. Ideology was not the factor in the defeats. The IL Dems have an excellent ground organization and GOTV and that is the common factor in all three races.