WARNING: WALL OF TEXT
I saw in the description that the soldiers received military training and are armed with submachine guns.However, in the game play, they seem to fire rather slowly, and you can hear a single blast instead of say...a titan's or an executor's rapid fire.
A submachine gun is a small and compact machine gun, but it's a machine gun nonetheless. The gun has to be fully automatic or have burst capability. Wouldn't it be more accurate to say that the soldier is armed with a "carbine," which is a short rifle?
You might not like this, but what he's holding is actually a pistol, believe it or not. Pistols don't necessarily have to be handguns. Just Google "ar pistol." A pistol can be the size of a submachine gun or even look like one, but like a carbine, it does not have to be automatic. If you're not that technical, or you don't want to call it a pistol, just call it a carbine, which is a cut-down or short rifle. A carbine can be short AND only semi-automatic, which is what the soldier has. Also, he's a soldier. They rarely use submachine guns. The fact that that's their main service weapon seems odd. Then again, this is an alternate reality...
In short, a submachine gun is...well, still a machine gun of sorts. You can't call something that isn't automatic a machine gun. Then again, you could say that the soldier DOES have a fully automatic gun, but he set his submachine gun to "semi-automatic." That's actually a really spicy way of splitting hairs. (Hint hint. Wink wink.)
In case you're wondering "who cares, " this might seem like a trivial thing for others, but as someone who shoots often, things like this stick out like a sore thumb for me. (Don't even get me started on gun "clips") Anyhoo, I figured I might as well put in my two cents.
Tl;DR Soldier doesn't have a submachine gun because his gun isn't automatic. He has either a carbine or a pistol.