We think a lot of the blame lies in the field of the historical role of "farmer". In western culture, the wolf has traditionally been vilified by the people. And if the regular wolf is evil, imagine then how much more evil the human that turns into a big and nasty wolf would be. Big cats just never were common in the traditional western culture, thus they did not develop the same fear.

Today of course, big cats are visibly much more dangerous than wolves ever were. But that doesn't truly sink in for most.

The werewolf/vampire conflict is also a reason. the other weres haven't had a traditional enemy.

With less writing covering them, the other weres require more thought and study to use, as there isn't a flood of available sources for how they work and what traits they exemplify. A werewolf can both be a lone wolf and a pack animal, which gives an author/artist more options when choosing the variety to use. A werebear, for example, doesn't have a natural pack mentality.

We think all sorts of weres can be good if done right. Yes, even a were-muskrat.