Its the predictability of the bat, its only dangerous under very certain conditions. If you have a bat and a guy comes straight at you, that bat has no power. You need to step and swing with the bat for it to become deadly, the knife needs almost nothing in order to a kill person.
Even though I would prefer the knife, I think you are underrating the bat here. It's not like a police drill where the badguy has the element of surprise on his side, it's a deathmatch. The batguy knows the knifeguy is coming to kill him, and he knows he has to make his shot count. And even though winding up will but you in an awkward and somewhat immobile position, the blow from the baseball bat will be hard as f*ck. It will be deadly. The question is, can he time it right to where the opponent is not to far away and not to close, about 4-5 feet would be great, and can he hit the knifeguys head or neck, in which case knifeguy crumbles to the ground and the fight is all but over. On the flipside, can the knifeguy effectively use faints, put the batguy off balance and darth in to shank him , while dodging the blow. If think more often then not, knifeguy will pull it off, but I think it's close.