I think there are nice innocent people in their world, but it's just that MC is in full on revenge mode and he doesn't have the time/mood to go happy hanging out reuniting whatever with whoever nice he knew for now, and since it's a dark story following the MC's revenge, it's reasonable to see only awful people who deserve suffering from the vengeance shown because they are the most relevant subjects to the objective for causing the MC to walk that path through betrayal whatever that only their torturous death could bring some closure/peace/satisfaction/etc to MC. So yeah, IMO, basically nice people exist in the setting but are not the focus, there are only victims like that to maintain the dark cruel depressing atmosphere to make the revenge more rewarding/satisfying for the readers. So I guess shifting focus to nice innocent characters that are still alive would "cool down" such vengeful feel/mood and it's probably not the direction of this series the author wants to take. Maybe rationally MC doesn't want to involve them in his revenge too as a way to protect them from becoming hostage etc too.