I'm surprised the list of "substantially similar states" wasn't limited to MA, NY, NJ & CA to be honest.
Similar to how Massachusetts has its approved firearm rosters, which manufacturers must go out of their way to appease, resulting in most brands deciding that "selling in Massachusetts isn't worth the hassle," I'm sure Illinois sending out its laundry list of requirements to other states results in even similar states not wanting to bother, which, in the end, is probably part of the desired outcome.
Guys...the first thing I did when I moved to Indiana, less than a week in, was buy a transferable firearm and a suppressor.