Time to be a smart ass:
There are always reasons something happens or does not happen.
There is no way to doupt that 2h ,1h+shield and polearms had large popularity in the window of time crpg takes place. There IS however not much proof that dual wielding weapons in that same era gained a lot of popularity. Since these people back then fought wars to the death and did not play games, (although im not a time traveler) Im pretty sure they used those weapons that prooved to be the most effective ones and not these that would give the most fun to carry into battle. In conclusion Id say that dual wielding simply was not as effective as other weapons we already have in the game.
BUT: Looking at the 1h weapons equipment page or any other, I see tons of weapons that are not used other than for teh lulz. Simply because they are not as effective as other ones. "Its not historicly accurate" sounds like implying that people back then didnt "unlock" the ability yet to be able to think about puting one weapon in each hand.
That said: If dual wielding is simply not vastly effective, as plenty of other things in the game right now are not as well, just add it but balance it in a way that it is simply not vastly effective. I really dont see the point here to not implement it just because there are no big battles in history that show its existence. In real life i might paint the fletching of my arrows light red to be able to see them flying at greater distances better. In real life, if Id carry a bow in a castle, knowing there could be an enemy around the next corner, Id definitly hold the arrow already nocked, saving me much time that could be the difference between life and death, instead of starting to pull it out of my quiver just when someone jumps around the corner 2m infront of me. Its not like god comes down from the heavens and sais "Mortal, you shall not do this, as it is not written down in the history books".
Personaly I dont care as Im not a melee. But why not give melees a new toy if its not gamebreaking ?