While the samurai wore daisho, it was extremely rare for them to wield daisho. The two swords simply have two different functions, and most of the idea of a katana-in-one-hand and a wakizashi-in-the-other is assumed by people without a full picture of how they were used. It's more likely that a katana would be used one or two handed as a primary weapon and the wakizashi as a backup, or for close quarters fighting, or for other uses.
Two-weapon fighting just wasn't done that much in history anywhere. Because it's frankly hard to do, and most people lack the coordination to ever get very good at it no matter how hard they try.
