Its my understanding that the NRA views that as a "divide and conquer" strategy by Chicago and they've rejected it multiple times in the past.
A few years back, it looked like a proposed law for concealed carry had a good chance of passage. However, it was amended to allow individual cities and counties to opt-out. Had it passed, Illinois would have been a confusing (and dangerous) patchwork of counties: some in which it was legal, and some in which it was a felony.
of gun owners cried foul when the NRA walked away from the table on that one.