You don't always have to join Zug or Urk. Often you can let them fight it out and remain neutral, or choose how much of your resources to commit to the fight. Urk needs everything you have, whereas Zug would be perfectly happy to see you do nothing and in most conflicts most people stay out of it. Because of this Zug can't afford to go around rewarding everyone for not joining Urk the same way Urk can reward you for joining him.