Maybe the defensive players have an edge in that department because their strategy is simpler: if they are in a bad day, they can stick to chasing down every balls back, as good as they can. On the other hand, an offensive players have to take a lot of decision regarding shots selection.
In both case, the players have difficulties to execute correctly their shot. But in the second case, they have also some difficulties with their game plan, which is more demanding.
Overall the player who win the most when he plays the worst is the one who has the greatest margin against his opponent.