Every board game has rules. Every card game has rules. Every athletic competition has rules. Every election has rules. Every society has rules. WHY?
Rules establish the object of the game and provide the organizing principle for fair play - rules establish what is and what is not acceptable conduct in the game. You have to take turns, you cannot look at someone else’s cards, you cannot challenge or dispute the referee, you cannot vote twice - and there are penalties for not following the rules in every game. If you don’t play by the rules in a game you either lose on points or are disqualified.