Human beings are armed by penetrating weapons . A wound inflicted by them heals badly. Moreover, the weapon can broke and remain in the wound. Being smart, desperate human usually strikes before death. Yes, tiger always win the battle. But its chance of losing the war is too high.
Therefore for hungry tiger human is about the same as poisonous porcupine. And human scent (awful mix of scents from its habitat) is a good substitute for adder's hiss.
Of course it is all about pre-civilized times.