Also, how could you 20 hand a weapon? There isn't room on the handle. Still there are reasons they aren't proficient with many weapons.

Owrtho
It's the rules, they don't have to make sense. How can you have a colossal++++++++++++++++++++++++++++++ mouth on a medium creature?The rules are the rules; you have enough hands, you can wield the weapon, and you get .5x to strength extra for each hand.