These systems aren't purely algorithmic and the tribal council / althing / whatever body judges the cases understands that people will try to game them. In old Iceland, murderers from wealthier families were often hit by massive weregild, precisely in order not to repeat their crimes.

"Life for life" is, across the entire history and spectrum of cultures, a minority position, for all sorts of reasons. Including the one that you don't want anyone who kills in cold blood (the executioner) living next to you.

Even societies which had the capital punishment usually tabooized executioners, or forced the job on slaves etc.