Anyone care to explain Blood Scent?

Recently saw Warwick mentioned in the patch notes, as there was a change to how Blood Scent works, but I have to ask: Why is it still a toggle? Why not just make it a straight-up passive? I don't play Warwick a lot, but when I do, I often will find myself accidentally hitting E in a fight and losing that critical movespeed that I need to finish a champion off or get away from death. It doesn't seem like there's really a good reason to have it off at any point in time either, as there are no real drawbacks. Maybe I'm forgetting something, but if not, maybe it's time to take away the toggle on it?