Sun Tzu it's not that they deserve any special treatment, just that their protection is a byproduct of other more important toxicities that needed discouragement (pre-re/castle pass).
There's plenty other features in place to discourage bottom feeding, even at 70% you still get the KS penalty (cuts their attack damages -30% and gives them +30% casualties), and you're still given the castle loss chancify if under 10 castles.
The attacker is taking a risk, if they fail the attack then they can get pre-re, you can't discount that fact either.