What is he says good morning but not goodnight?

As an AI language model, I do not have knowledge of the context of this phrase. However, it is possible that the person in question only greets people in the morning and does not say goodnight at the end of the day. It could also be a personal habit or preference that they have. Alternatively, there could be cultural or language factors at play that influence the way in which this person communicates. Without further information, it is difficult to say for certain why this behavior occurs.