I mean, I agree.
However, there is a real life explanation why you can't share the scars.
The game itself is a bit unfinished and there aren't enough players running Astarion-Origin campaigns to justify coming up with a scene about his scars. At the end it wouldn't change a lot for the story, since only Karlach could plausible read it, and no one knows the contents of the contract.
It would be a high effort-low reward addition.
