like the joker on the old batman show would slowly dip batman into acid...Why didn't he just kill him while he was tie-ing him up?
Well, because if the villian killed the Super Hero. Then there wouldn't be a reason why they still do the show. So if Batman died, then no more Batman Series.
Because if the heroes all die, then the point of the classic hero story, "good triumphs over evil", doesn't get across.
To savor his victory, I suppose. Also to make it more dramatic.
That's a goood question......Hmmmm.......