You do know that a claymore weighs like like 20+ pounds. I would like to see you swing one with one hand, none the less one with each hand at once, and do it repeatedly more than 0 times.
Claymores on average weighed 4-6 pounds. Decorational and positional weapons weighed sometimes 8, but were not meant for combat.
The reason one could not dual wield claymores is thanks to leverage. The weapons are too long to be used effectively, in addition to being balanced for two hands.
Now, some swords, like Bastard Swords, were meant to be used both one and two handed, although I highly doubt those can be dual wielded, as, once again, they are a bit heavy (4-5) and are weighted differently. The main reason to use two hands would be more power or control over the blade.