Have you read about illusion of control (search for elevator door button for one well known example)? If we take the idea that recommendations are really hard and dislike button doesn't help at face value, wouldn't it still improve the user experience to give them the illusion that they can directly affect the recommendations?

I'm not really convinced about recommendations being hard, though. Pandora could do them a long time ago, Netflix had good recommendations at one point but not since they dropped the star ratings and at some point Amazon wasn't that bad either.