Assume that after elections two coalitions are formed. Let’s call them Player1 and Player2. Player1, although they can rule, wants Player2 to join them in forming a Government. Player2 refuses and aims for reelection where they believe that they will be in a better position. It is all a game of success and failure on the government to be formed:
So in the case where Player 2 believes that Player 1 cannot make it alone, they bet on their downfall in order to win the next elections whenever they are. And while Player 1 knows that they cannot make it, even with Player 2 on board, they push for their participation so as to make them irrelevant too in the next elections.
Any similarities to present day politics is purely coincidental.