If I get a bad review, I'd really like to know why it is I'm getting that review so that I can improve my game, or at the very least make sure I make a better game next time. A negative review with nothing to say just isn't helpful at all. Moreover, if users can leave blank negative reviews, it makes it hard to distinguish an actual negative review from trolling. Adding this feature would make it so that developers can get actual feedback on their game when a user leaves a negative review, and helps to distinguish actual negative reviews from trolling.
Obviously, there's some issues here -- requiring users to comment would take away the anonymity that allows them to leave a negative review in the first place. A solution to this is to allow users to make a comment private, so that only the developer can see it.
