No reason left is probably because of the retaliation culture or because the owner of the post isn't the target, but the owner of some bid not used was.

I've run a test once doing 1% dust sized downvotes on posts upvotes by a bid not. Got me quite some 100% retaliation down votes.

I'm all for down votes as way to curate and attenuate bid bots, but the retaliation culture on here is truly ruining the idea.