The rating for individual player depends a lot on the opposition, so does game shape (if not in the same week). I am not at all surprised to see players with better stamina get better rating. Better stamina means to me that they can last longer on the court and play close to their full ability. This is probably the same reason why I have observed that players with poor stamina (3 or lower) tend to play better as a backup player (less min on the court).