Feelings of satiation are caused by many factors, including neural signals from the gut (which supposedly is not enough to explain the alleged obesity set-point), hormones due to blood levels of carbohydrates, and also blood levels of amino acids and lipids. In addition, they are caused by levels of insulin, glucagon, and cholecystokinin, among others.

The desire to eat more may simply be because the rat wants to maintain the levels of these hormones that they're used to. There is absolutely no reason to think (based on these experiments, at least) that there's a set-point that is based on 'healthy weight for your height/age, plus or minus a genetic factor'. In fact the very article you linked strongly agrees with this viewpoint and disagrees with your view.

The reason I mentioned the bait-and-switch is because the mechanisms controlling eating in humans are very likely, in my opinion, to be different from rats. Note that this isn't the same as saying the reasons are disjoint. It could be that we have the same underlyling mechanisms as rats, but also a large psychological component on top of that, that effectively prevents being able to directly compare rats and humans.