I think it's because humans don't fight much with their mouths. We mostly fight with our arms and more rarely bite and rabies just promotes hyper aggressiveness, of which, these symptoms are exhibited in infected humans.
If restrained instead of sedated a human does get very aggressive, flailing their arms, screaming and hurling insults, even at loved ones and family members. I think given the opportunity there would be some biting, but less often than animals, because again, humans primarily use their arms for violence.