Sure, we players are too dumb to know whether an animal is asleep or sick. The fact that there is a big red icon over them if they're sick doesn't help either. Better cancel sleeping so the players won't get confused and throw their console/computer out of the window.
Sorry for polemic, but how in the world can you accept such an answer?
I think you need to keep in mind that a lot of people aren't very smart. Also the other big reason is that this games main audience will be kids. Not all kids are that smart. Many learn as they grow. Some are just naturally smart and quick to pick up on things.
IMO this is a legitimate answer considering what I said above.