Because GM wanted to use the A-body designator for the FWD cars, so in 1982, they went from that SAE to metric wheel stud, and changed the world by magically making the A-bodies into G-bodies. 81's were sort of "tweener" versions as it were. New body styling but still technically an A-body. Nothing really changed in large part except the designator.I've never understood the change from A to G when 95% of the parts the same - beware of the wheel stud change from SAE to metric. AFAIC, a 79 Cutlass or Malibu is not what I consider an A-body - but what do I know?
Sort of same thing happened in 1985 for Oldsmobile though just a name change. Up through 1984, the A/G bodied Calais was the Cutlass sport version. The Calais was going to be its own model for 1985, as a FWD smaller car. Thus, they needed a new name to use for the 1985 G-body Cutlass sport version. So they used the older namesake of Salon to take the place of the RWD Calais. Then it went away at the end of the 87 model year.