It’s some weird misconception that, like heaven, hell needs to have some sort of ruler. Naturally, the intuitive thing is to pick the mightiest entity in there and declare it the king, because that’s kinda how we perceive kingship. Aside from the fact that literally all the entities in there are convicts imprisoned by the final judgement, at which point there’s only one eternal king left:
It’s a fucking sea of fire, what the fuck are they gonna rule?
Inferno has the Devil frozen at the heart of hell, struggling in vain to break free, his beating wings producing the freezing wind that keeps him trapped. Not my idea of a ruler, to be honest.