The idea is to make it possible to change the difficulty for each dimension trough the config file, giving modpack developers the ability to set certain dimensions as more of a late game requirement, like making the base level of mobs from "The Aether" higher then the overwold or making mobs on the nether level up faster per distance to simulate the level of the mobs you would get if you build a portal at that location.

I just learned that this is possible trough datapacks, im sorry