Well the problem isn't that you can't come up with a reason, it's that you have the intuition that it in all honesty it won't be the reason.
Parrottmath, you must be a great educator, because I almost never got back the reason I got exactly a 90 on a paper instead of 95-100. Believe me, I tried on occasion, but I have seen the wisdom since then in there not being a good answer. Even the GRE has an essay section that is graded holistically, where really it comes down to what does the paper feel like to someone with a (hopefully) highly developed intuition. Essays, games, and movies are such complex works that if you deny that when you are scoring the game you are relying on a heuristic, an emotional memory of a long experience or many experiences, you are in effect deluding yourself with your mind's own explanation mechanism. These medium are about intellectual or emotional satisfaction, and pinpointing the flaw can be more apt to end in error or just intellectual confusion in many cases.
The problem with just repeating the results of gameplay is that the emotion captures holistically how ever many hours they put in to it. Even doubling that time doesn't change the fact that you are encapsulating an enormous amount of information in a feeling.
People look down on the response it feels like this or that as a reason. I am reminded of how Garry Kasparov said he went about playing chess. He did an extensive amount of preparation and after that he played "by sense of smell", where emotional responses to ideas likely encapsulate thousands of hours of experiential wisdom. People often think the best chessplayers calculate better than the rest, but really chess calculation is intractable. They just sense what the most reasonable moves are based on intuition, feeling, or "sense of smell". They calculate better, but only because the best moves are sniffed out with less effort than the common player. (One chess champion, Vasily Smyslov, was known as "the hand", because he had such an intuition it seemed like his hand knew what to do and just reached for the right move)
David Hume wrote "Reason is, and ought only to be the slave of passions", and he probably wasn't thinking about this, but it is another way in which this sentiment is incredibly wise.