Motivational reasoning... more drastic than the mere decimation (10% reduction) used by the Romans in the waning days of the Roman Empire.
There have been several reports of unpleasant executions of retreating fighters in the past for exactly the reasons you said. Word gets around.
The Reds decimated (classic definition) their own ranks during the Civil War for units that lost a battle or that retreated. I can’t stand when that word is used to mean “destroyed.” It shows the lack of education that infuses our society due to several generations of federal and union control of the public schools. It also shows the uselessness of English dictionaries since the Webster’s 2nd International.