I believe this is intentional, much like the Necromancers that you can only use it on corpses that have died recently and within a specific range of your character. So you can't just run into areas with pre-dead bodies and get something out of them.
Someone told me if you have for example 10 corpses around you and a necromancer uses one of those for a skill, the entire 10 corpses can no longer be used for repentance.