-your opponent looks across the table at your list and believes, correctly or not, he has no hope of winning. Thus he deploys and engages in such a way as to produce the most minimally scoring game possible.
-your opponent realizes after deployment, correctly or not, that he screwed up, has no hope of winning, and then seeks to minimize losses by not engaging.
-you are clearly winning the game, but score no points for ships limping away at 1 hull. Knowing this, your opponent 'bugs out' denying you points.
Your opponent is trying to maximise his score for the game and overall score for the tournament. Why would you expect him not to?
Look at it from his point of view, he is earning as many points as he can.
So, again why is the way he does this a problem? He isn't cheating, he is just making sure then every point he gives away is earned. What are you doing to earn those points?