Those villains may have lost themselves in their desire for power, or had little to no redeeming qualities, but on a fundamental level they are capable of humanization. There was something that pushed them to think the way they did because we know there aren’t actually humans born as evil as them, and their stories rarely if ever treat them that way.

Makima isn’t a human, or even mortal in a technical sense. She axiomatically had no reason to view life the way a human would, even more than if one attains godlike power. There was likely no point she could experience the vulnerability of growing from infancy, senescence, etc. There’s no inner humanity you could imagine appealing to, unless you genuinely think you could do so for the gun devil, bat devil, eternity devil, or other devils that don’t look like supermodels. She is actually a character who did desire an equal relationship/wanted to help humanity, sure, but there was no question of her methodology changing. The circumstances that could have allowed for redemption were centuries if not millennia in the past and impossible while surrounded by devils in hell.