Actually, Lord Liu had his own troubles to vent. He had initially vowed to fight thieves with thieves. However, it turned out these robbers were quite poor. Even after raiding two large robber tribes, the only gain was a small increase in population, with no other spoils.
Clearing out smaller tribes wouldn't mean much except for getting his warriors' blades a bit bloody and stretching their muscles.
But how could Lord Liu confide such things to others, beyond his three closest girls, without tarnishing the dignity of a lord?
The slaves of the wilderness are arguably the least expensive slaves on the Aegean Continent. The most valuable ones are beautiful young girls and skilled craftsmen, while the least valuable are menial laborers without any particular skill.
The robbers of the wilderness are tall and sturdy, making them ideal for hard labor. But without any mines in the wilderness, these captured slaves have no value beyond consuming food.