Well it really depends on which show/movie your looking at , Im Twilight its because the vampires kill people and the wolves are the protectors but in vampire diares its because there both uncontrollable things so really it depends but form all the fiction things i have read over the years its more of just a mortal enemy type thing that there naturaly born to kill each other
The werewolves came into existence as protectors of their tribe. Then a pair of vampires attacked the tribe and another neighbouring tribe. Those vampires were the most dangerous enemies the wolves had ever fought. They've been natural enemies ever since.
