Immortal Life Is Cheap: This might be the case in the noetic-backup-having modern world – and to some degree is, when one can send deliberately-disposable temporary forks of yourself in designed-for-the-situation temporary bodies into dangerous situations, and suchlike – but the cultural attitudes were formed back in the day when immortality was still just Type II Undying, and law and custom haven’t been altered.

And in Type II Undying-land, immortal life is very expensive indeed, especially since healing and regeneration weren’t always as effective as they are in the modern era.  It is from this period that eldraeic, and hence Imperial, law got its truly draconian attitudes on the topics of murder (because you’re removing a lot more life from an immortal than you are from an ephemeral, not that the penalty is any different if you happen to kill an ephemeral), battery (again, because your victim has to live with the damage for a damn long time), torture and rape (because your victim has to live with the trauma for a damn long time).

Which, to bring this full circle, probably does mean that Immortal Criminal Life is Cheap, because truly draconian in these cases generally means “being made dead”.