This is a misunderstanding on your part. The king is picked by the Kingmaker each night, and the king can be town or scum. The Kingmaker himself is always town though, and if the Kingmaker dies, a random town player will become the new Kingmaker. So if scum were to kill the Kingmaker (who is confirmed town) each night, they will have to contend with a new Kingmaker, who will also be confirmed town, every single day. The other option is, they leave the Kingmaker alive and have one single confirmed townie to contend with for the entire game, while the rest is fair game.