The wolf is familiar; wer preserves an older word for man.
Old English werwulf combined man and wolf. The animal component remains easy to recognize, while wer preserves an older word for the human half of the creature.
Middle English is omitted as a separate stage.
Sources
- Merriam-Webster: werewolf
Word History and Kids Etymology give wer, man, and wulf, wolf.
- Online Etymology Dictionary: wolf
Wolf is from Old English wulf, the second element of werewolf.