While originally thinking they were some kind of "fledgling", I read that Bloodfiends were older Vampires that had gone insane and degenerated into mindless monsters. I'm assuming this affliction is unique to the Noxiphilic Sanguivoria strain. This clearly doesn't happen to all of them, but is there a specific reason it happens to a good many of them? Is it from lack of feeding? Lack of control over their urges?
Rinnegan Dovahkiin: Daedric Prince of Balance