I'm pretty sure it's more just a limitation in the engine/coding. The game doesn't know that the people who own those things are dead, so it's still flagged as theft. I guess they could go in and flag each individual item with a specific owner along with it's own karma and flags for if they're alive or dead, but that honestly seems like a nightmare. I'm sure their time is better spent elsewhere.
It's not like Karma matters anyway.