We understand things differently. I think comments are for your emotions after playing a specific game, and ratings are for showing what you like or not in detail. You don't understand that this was my emotion after playing this for more than an hour with some short breaks, and after all this time I don't like this game. Comment = emotion. If I would think that comments are for "constructuive criticism", I would've posted something else.
Plus, no one says "you can only post constuctive criticism here, nothing else" before you post your comment. That thought also looks so simple to me, just try to understand that people think differently, it works with every person, meaning if most people think this way a different person don't have do think this way too.