Knurling on parts that see constant friction movement (like pistons, valve guides, etc) has a down side, knurling reduces the contact surface area and the part will wear quicker. Knurling a part like a crank snout to restore its diameter is different since the balancer is a press fit and there's no constant movement.

As I said earlier, the factory was reluctant to scrap a part if it could be saved with a simple procedure.