Michael Barone offers this explanation which BestView found enlightening.
How did he become Governor? Family connections: “Blagojevich is the son-in-law of 33rd Ward Democratic Committeeman Dick Mell. Ward committeemen are hugely important in Chicago politics: Dan Rostenkowski and his father had been the 32nd ward committeemen from 1935 to 1995; the ward committeemen from the 11th ward since some time in the 1940s have been Richard J. Daley, Richard M. Daley and John Daley; the 13th ward committeeman Bill Lipinski, retiring suddenly from Congress in 2004, was able to get the Democratic nomination for his son Dan Lipinski from a group of ward committeemen despite the fact that Dan Lipinski was a political science professor at the University of Tennessee and hadn’t lived in Chicago for years.”