Because the look of the thing is everything:

Illinois Gov. Pat Quinn is once again calling for legislation that would ban the sale of assault weapons and high-capacity ammunition magazines.

[ . . . ]

Quinn is specifically pushing for the passage of the Illinois Public Safety Act.

Under that proposed act, holders of Firearms Owners Identification Cards who now own assault weapons would be able to keep them. But they wouldn’t be allowed to transfer or sell them – except to a family member.

And, by implication, this would require registering them.