I agree that pleasure has something to do with learning, but I don't see why the "urge" or "desire" mechanism couldn't help us learn to do rewarding things without the existence of pleasure.

Without pleasure, things could work like this: If X is good for the animal, make the animal do X more often.

With pleasure, like this: If X is good for the animal, make the animal feel pleasure. Make the animal seek pleasure. (Therefore the animal will do X more often.)

So pleasure would seem to be a kind of buffer. My guess is that its purpose is to reduce the number of modifications to the animal's desires, thereby reducing the likelihood of mistaken modifications, which would be impossible to override.