Answer:
They have been punished for doing so.
Explanation:
According to the Social Cognitive Theory, by Albert Bandura, learning takes place in a social context through reciprocal interactions of people, environment and behavior. Observation plays a big part in this theory where reproducing learned behavior will lead to rewards.
From this perspective, we can say that the students who turned in their homework assignments and were not rewarded as promised were actually punished for doing so and the students who didn't turn in their work but observed what has happened were negatively influenced by it.