They probably aren't carrying ammo yet. Often when Soldier's deploy they have to carry their weapons at all times but aren't issued ammo until they get somewhere hostile, it minimizes the possibility of negligent discharges. It's very possible and probably likely that a majority won't be issued ammo at all as it's more a show of force than anything.
why does that guy have no magazine in his gun ?
They probably aren't carrying ammo yet. Often when Soldier's deploy they have to carry their weapons at all times but aren't issued ammo until they get somewhere hostile, it minimizes the possibility of negligent discharges. It's very possible and probably likely that a majority won't be issued ammo at all as it's more a show of force than anything.
I always thought one crazy lefty taking out an entire battalion of soldiers who weren't allowed to have ammo would fix this.
Also there probably are selectively armed Soldiers like MPs.