I would imagine it's to even it out between those who have lots of cold weather starts, winter gas and slushy crawls and those who have warmer more efficient operating conditions.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
The mason-dixon line where it crosses I-81 is in a mountainous region. I believe the requirement was so that you could not create a team of cars running in Florida, in optimal conditions, running ethanol free gasoline. This requires that a team consists of vehicles operating in different climates and environments.