I found a news story from when the lawsuit was filed that explains it pretty well:
SAF Sues Illinois Over Ban on Carrying Guns for Self-Defense BELLEVUE, Wash., May 13, 2011 /PRNewswire-USNewswire/ -- The Second Amendment Foundation has filed suit in federal court in Illinois, challenging the state's complete prohibition on the carrying of firearms in public for the purpose of self-defense.
The lawsuit alleges that Illinois statutes that completely ban the carrying of handguns for self-defense are "inconsistent with the Second Amendment."...
"Illinois is currently the only state in the country that imposes a complete prohibition on the carrying of firearms for personal protection by its citizens," said SAF Executive Vice President Alan Gottlieb....
"Illinois is the only state in the country that completely prohibits its citizens from carrying guns for self-defense," Jensen added...
"Every other state has some kind of regulatory scenario," Gottlieb noted. "Even in Wisconsin, where there is no concealed carry statute, the state attorney general has recognized that open carry is legal....
and please understand I'm not against concealed carry laws, I just don't think these news stories allow the average person to understand the outrageous nature of the current law in Illinois.
concealed carry used to be a crime a lot of places, but that is changing or has changed.
It was assumed that if you hid it, you had nefarious reasons.