Well thats easy, We are sentenced to be pawned off to a Penal Legion or executed later which sounds awful so... we join you and we get to be free? Deal

they are all disreputable anyway like Acid Dogs or other hive gang criminals tossed into imperial service. so the idea of being pirates or whatever would be more agreeable than being executed. It would mean a few small edits to the CS nothing important, the flavor would be the same. Except the first stop he would demand would be the Armory.