It was originally decided that way because of the wind pole.

Hear me out (and keep in mind that when i say 'pole' I'm not necessarily referring to the pole itself, but the region)

The wind pole covers the north in ice, but the wind can also carry intense, searing heat (I live in Texas - trust me on this). Meaning that if the sun were to ever set or rise in the north, the wind would carry his intense heat throughout the land instead, melt the ice, and lead to intense flooding extremely quickly. The fire pole doesn't need the sun for heat, and it's so dry that it can cool...