Why does a conditioned response disappear when the expected food is no longer presented?

In the context of animal learning, the disappearance of a conditioned response when the expected reward is no longer provided is known as extinction.12

In both classical and instrumental conditioning, the strength of a learned behavior is maintained by reinforcement—the presentation of an unconditioned stimulus (such as food) or a reward. When this reinforcement is consistently withheld, the association between the conditioned stimulus and the reward weakens. Consequently, the animal gradually ceases to perform the conditioned response because the behavior is no longer functional or "instrumental" in obtaining the expected outcome.12

Essentially, extinction serves as a mechanism for the animal to adjust its behavior when the environment changes and the previously learned signal no longer reliably predicts the arrival of food.1