It is because it makes the game extremely unfair for non-$300 donors when pvping a $300 donor. When the non-donor dies, he or she loses his or her full inventory+experience. Yet, if the $300 donor dies, he or she loses nothing. It makes non-donors wage substantially greater stakes when compared to their donor opponents.
Apart from that, it says in the rules that this $300 perk does not include deaths while pvping.
Apart from that, it says in the rules that this $300 perk does not include deaths while pvping.