Mainly so it wouldn't create another PK mob outside of a building.
>>Classic PK thought process "Oh this guy/gal hit me, I am going to hit him back."
By the point that the person actually kills him/her, about 5 other people are involved. Pretty sure this is how mobs are started, correct me if I am incorrect. (Minus the blob. That is a monster of its own. I am mainly talking about the Mod and Swamp mobs.)