Short answer: Because they’re both awesome.
Long answer: When I was a teenager, I read a lot of books about wolves, which invariably started out, “Wolves are not the monstrous beasts of legend, but interesting and misunderstood social animals.” These pro-wolf books would go on about how wolves really don’t kill people, and they’re not horrible and fearsome, and that people’s fear of them is really just bad PR. As a teen, I took this for granted. Well of course that’s the whole story. Bad PR! Oh, those brothers Grimm, look what they started!
But the truth is, we have a primordial fear of wolves because wolves are giant predators, and we are big chunks of meat. Maybe if you’re from India, you have a primordial fear of tigers. I’m sure sub-Saharan African oral traditions are peppered with accounts of lions that pick off innocent people. The Aztec warriors didn’t dress up like jaguars because they thought spotted cats were cute, they admired jaguars because jaguars are really good at killing people, and that’s what they wanted to be too.
So maybe wolves haven’t really been the scourge of the night in the past couple of centuries, but for millennia, the wolf was the most dominant predator of the Europe. It ate people and stole livestock (which can be just as brutal, if those livestock are all that stands between you and starvation for your family). Wolves did this for so long that the wolf as beast idea got ingrained into the collective cultures that descended from those terrified pastoral peasants of yesteryear.
So when a writer incorporates wolves into her story, she doesn’t have to create a monster from scratch. Wolves already have huge cultural baggage along with them, a Jungian history of fear and beastliness: ‘The wolf at the door’, ‘Howling wolf’, ‘alpha wolf’,‘Lone wolf’, ‘Werewolf’ (And of course the sidecar of predatory aggression, sexual aggression) ‘wolf whistle’.
Not only that, but wolves have a biological hierarchy that’s familiar to many people. We know that the alpha male and female wolves are the ones that breed, and that the beta male and female don’t, and that the gamma wolves are usually outsiders. Although alpha really corresponds most closely with “mother and father” and beta is closest to “non-breeding family member,” (like a grandparent, or an adolescent child) no one really minds if you tweak it to fit in with your were-, talking-, or otherwise magical-wolf society. You can make the alpha male wolf a king, and the alpha female a queen. Convenient, isn’t it?
When the naturalists learned how human-like wolves were, they took the familiar beast of legend and rewrote it into a noble savage of the wilderness. Modern readers think of a wolf, and they think of a beautiful untamed animal, fur sleek and healthy, staring at the moon in some picture-postcard scene. Wolves are the perfect vehicle to dump all our fantasies of unspoiled nature (especially now that white America found out that Native Americans, inconveniently, are actual, complex human beings, instead of noble savages). The modern wolf doesn’t carry off sheep or eat biscuit-toting granddaughters. The modern wolf, when it’s not a spirit guide to New Age mystics, suffers in lonely splendor, symbolizing the wild world we lost when we got civilized.
So, in short, wolves are awesome. They can be so useful. If you have a sword-swinging warrior who wants to inspire fear in his enemies, all he has to do is call himself “the wolf” and everyone will be expected to shudder. If you want a shaman or druid who has Mother Nature on speed dial, have him dress in the skin of a wolf. If you want a smoking-hot high school senior to have a nice touch of bad-boy spice, make him turn into a wolf once a month.
And here’s why you shouldn’t use them. Yeah, you read that right.
Imagine you’ve been asked to make something for a bake sale. You decide to make chocolate chip cookies. Chocolate chip cookies are awesome. Everyone loves them. My brother, for one, insists that chocolate chip cookies are the only true cookie, and every other cookie (with the possible exception of double-stuf oreos) is a rude imposter, a blight upon the good name of cookie, who does not deserve to reside within a cookie jar.
So you make chocolate chip cookies. And guess what? Everyone else made chocolate chip cookies too! Some bake sale! Where’s the variety? What about those people who don’t like chocolate? (Yes, they exist. Sad but true.) What about diabetics who were hoping for something sugar-free? What about the people who wanted to see what you could make that was, well, a little different? Vanilla crèmes and pomegranate cupcakes and macadamia brownies and ginger brittle may not be as good as the ol’ standby, but in a bake sale that’s crowded with Nestle Toll-House, isn’t a blueberry-lemon bar going to stand out?
If you’re baking for yourself, bake what you like the best. If you’re writing just for yourself, go ahead and wolf it up. But you’re not really writing just for yourself, are you? You’re writing for thousands of people you’ve never met. You can write another werewolf story, people do like them, they’re a good standby, but you’re going to have stiff competition. All the marketing books I read say it’s hard to succeed by doing what everyone else is doing. Sometimes you can. Maybe your chocolate chip cookie, or your teen-wolf story, is so good that it will blow everyone else away.
But what if you went somewhere else with your animal symbolism needs? There are a lot of other animals out there. Dolphins and pigeons and beetles and clams and mice and pelicans and bighorned sheep have not been done to death. In fact, they’ve hardly been done at all. Stephen King wrote a book about sparrows. What kind of cultural baggage do we have about sparrows? Almost none. If he could keep me riveted and terrified with a three ounce bird, just think about what you could do with a badger.