Complex sentence: The soldiers of the frontier armies were paid less than their counterparts in the field armies; however the recruits may simply have preferred to stay close to home, and wanted higher pay if they were going to join units which could be deployed anywhere else.
Split into simpler sentences: The soldiers of the frontier armies were paid less than their counterparts in the field armies. However, this does not imply that the field armies always hired the most promising recruits; some may have preferred to stay close to home rather than to join units which could be deployed anywhere else.