OOC #2
I think it is because no villain sees themselves as a Villain. Good clerics doing bad things don't see those things as bad, so they don't question them, and thus, don't ask for forgiveness, etc. You also have to look at the god themselves. A Lawful Neutral god of Retribution could have clerics that are Lawful Good, Lawful Neutral, True Neutral, and... Lawful Evil. Consider that only one of those alignments is actually good, leaving a lot of grey area.
It gets even more complicated when you consider that this particular god can alao have Paladins in their service. As well as Anti-Paladins. You can have direct opposition in the same faith.
I personally am a fan of the gods of death. But not in the "oooh I'm creepy and creating an army of undead" way. I play a lot of warriors who kill a lot of stuff. They are perfect instruments for a god or goddess of death, and when someone or something kills them, it was their time.
To take a quote from a famous, fictional character, "I seen a lot of stiffs. Seein' one makes me, I dunno, wanna do stuff, or if there's a willing woman about. Not that a corpse gets me... it's just I put a lot of'em in the ground Preacher. And in my line of work we don't live too long. One of'em could be me is all."
I paraphrased it, but the point is that someone who follows a god or goddess of death doesn't have to be someone who is necessarily evil, let alone someone who wants to end life. A mercenary who kills a lot of people in the line of duty is perfectly acceptable to me.