I think it’s because it’s made out of Budget Steel, which is worse than the standard (Normal steel, not the dull replica) version.
You have stumbled across a replica of the almighty wakizashi. It isn’t cursed, but is poorly made and has significaly lower stats than the real deal.
its less cursed more a knockoff blade you find three kinds of weapons like that a knockoff. a poorly made/maintained real version and a normal version of the weapon. like a cheap mace. a lowquality but real mace and of proper mace