Cap'n Kobold
Hero
As has been pointed out, NPCs are generally built to follow a concept rather than rules-mechanics min/maxing.
In the confines of the underdark, a long range weapon is less necessary, and not having to reload every shot is handy - just not represented in the non-granular 5th ed combat system.
The reasoning behind the spear is that Derro are slavers. They gang up to give advantage on trips and hit or overbear their opponents while they are down. Remember that a lot of the things that they fight are Svirfneblin or Drow, not Strength-optimised PCs.
Also, spears or similar weapons are generally the primary weapon for soldiers and guards pretty much since organised warfare began. Its something that would delineate them from civilian NPCs who would likely also have daggers.
If the lack of mechanical optimisation in published adventure paths upsets you to that degree, change it to suit your game. That's always the Dm's prerogative. Give them shortswords or special racial rules.
In the confines of the underdark, a long range weapon is less necessary, and not having to reload every shot is handy - just not represented in the non-granular 5th ed combat system.
The reasoning behind the spear is that Derro are slavers. They gang up to give advantage on trips and hit or overbear their opponents while they are down. Remember that a lot of the things that they fight are Svirfneblin or Drow, not Strength-optimised PCs.
Also, spears or similar weapons are generally the primary weapon for soldiers and guards pretty much since organised warfare began. Its something that would delineate them from civilian NPCs who would likely also have daggers.
If the lack of mechanical optimisation in published adventure paths upsets you to that degree, change it to suit your game. That's always the Dm's prerogative. Give them shortswords or special racial rules.