Recently the ability to search sinking ships for loot was added to the game. Combat NPCs have a chance of dropping valuable repairs as well as otherwise unobtainable and very valuable skill books and permanent upgrades. More recently trader ships acquired more cannons making them comparable opponents to their dedicated combat peers and the loot table for combat NPCs was expanded to drop more rare upgrades.
The result of these changes is a severe imbalance of difficulty and rewards for a player sinking and looting a combat NPC vs a trader NPC. Currently on average a combat NPC will have more value in its hold in repairs, cannons, skill books, or permanent upgrades than a trader of equivalent strength will carry in resources or shipbuilding materials. Additionally combat NPCs give larger gold and xp bounties compared to their equivalent trader NPC. Since traders now have large armaments equivalent to their combat counterparts there is no longer any reason for a player to attack a trader instead of a combat NPC as the fight will be equally difficult and the rewards substantially less.
Two suggestions should repair this imbalance. First, trader NPCs should have repairs, cannons, skill books, and permanent upgrades added to their loot tables in addition to the trade goods they currently drop. Second, the gold and xp bounties of trader NPCs should be increased to reflect their new strength in combat.