That's because werewolves are stupid. And I don't mean that in the "I hate werewolves" sense, I mean werewolves are near-universally portrayed as feral and unsophisticated monsters. Which means they're difficult to sympathize with. Frankenstein's monster was sympathetic from the beginning.
Besides, there are tons of manga with wolf people, they just are usually the ones from Japanese mythology rather than proper werewolves.
Leviathan has both types of wolfman, incidentally.