Because the uses of a 1 Handed sword are a completely different monster to the uses of a Two handed sword. They are different Weapon Classes. Long Daggers and Short Swords I could understand. But Gladiator getting Two handed swords is preposterous just like Marauder getting one hand axes would be.
Each Weapon Class should be its own Weapon Class.
Mages Get away with it for one reason. Their Real Weapon is their AOE Casting. The Weapon they equip is just a magical focus.