@matsiyan, I think that’s due, to a degree at least, to firearms being generally more reliable, and grenades being better at clearing entrenched enemies than running in with swords/bayonets. Also, close melee is far more dangerous for both combatants. However, I can see grenades being a bad idea in shipboard combat, between the concussive blast being concentrated by the narrow corridors and either shrapnel ricocheting everywhere (it travels a lot further than most people assume) or plasma style grenades ruining a section of the ship, making the use of close-in weapons a little more likely.
A tonfa or baton style thing would be nice for most, though I worry they would struggle with combat armour or Torgoth.
One thing I think should inform the choice is the question of whether the TSN are trained towards incapacitating or killing in combat.