It wouldn't be that beneficial to gameplay. They'd just be slightly altered werewolves. And there'd have to be at least 1 or 2 more quests for it.
There's two forms of vampirism now, and no quests involving the vanilla strain that you have to do to become one.
Lycanthropy should not be exclusively obtainable from quests. It's a disease. It can spread through bites. Wild Werewolves (and the conspicuously absent Werebears) should offer a vector from which you can gain the affliction, just as you could from vampires.
Provided you survived the encounter of course.