Why wouldn't you use an assault rifle or a machine gun if you wanted to send as much lead flying as possible? It's like telling me I have to shoot something IRL, accuracy is of utmost importance then giving me a choice between a handgun or a rifle. I'm never gonna pick the handgun.I find it so hilarious that people are debating the realism of dual-wielding in a game full of unrealistic abilities.
It's a feature for those close-combat moments where you just want to send as much lead flying as possible.
It's got nothing to do with practicality, it's the satisfaction it provides.
Of course, I get the feeling a lack of dual wield has nothing to do with the realism factor. It seems more likely they put together a set of features they might consider and in the design process decided some of them weren't going to make it. DW didn't make the cut (or it did? I dunno... you get the idea).