Lord Death loves humans, and goodness is order, so him being sympathetic towards the side of good isn't that strange at all when you think about it. After all, what's the alternative? Insanity and fear, that's chaotic.

[Yes, she just said the god of death LOVES humans.]

And he guards the souls of the deceased when they pass on. [Lol what's an afterlife? She never bothered questioning where they go if they're not eaten by monsters.] I mean, why shouldn't a god of death want to safeguard the souls of humans? Reaping isn't an impulse, it's just a duty.