Melee vs. ranged weapons.
I am not sure if anyone mentioned the psychological part of this issue.
People do not like killing people. Ever soldier has to be trained to deal with this obstacle.
Killing from a distance is much less personal - you fire a gun and a small figurine drops dead, it is even more obvious for dron controllers - that is why we have so many moral issues with them trating combat as a form of video game.
Since killing is difficult and killing from a distance is easier fighting at close range requres even more training, stronger nerves/more powerful brainwashing etc.
This is one of many reasons why so many charges were successful, even when facing incredible odds. On paper many of assaults or charges couldn't possibly work, but enemies were paralysed by fear, wonder, indecision or mortal dread watching friends cut to pieces, bleeding, watching quickly approaching enemies apparently invulnerable to fire...
Even veterans can panic - it has little to do with fear - and fighting in close combat is never easy , but even more difficult to face experienced killers coming your way...
