Because firearms are ranged weapons, and there's nowhere on the station where we will need to use ranged weapons. Because with the total absence of any way for an intruder to enter the station, we are far more likely to shoot each other than actually use them for defense. Because with the increasing number of children on the station, they are most at risk.

[ He lets out a frustrated breath. Why are humans always so obsessed with guns? ]

There are any number recreation opportunities we already have or could make. This obsession with guns diminishes you.