The "to you" is generally used only where there is an audience (i.e. third parties listening or watching), especially if:
(a) there are several people to whom the "good morning" could be addressed, and/or
(b) if the audience cannot see the person to whom the remark is being addressed (e.g. a radio programme or a podcast).
The key point is that the greeting is directed at a particular person.
For instance, on TV or in a podcast, the phrases "Good morning to you Brian, and also to you Yunus", or "Thanks Brian, great answer, now over to you Yunus for your reply" are examples of when the "to you" would be appropriate.
The phrase might also be used in other group settings - e.g. in a classroom, where the teacher might say: "Good morning to you, Sally, could you please tell the class ...".
Note that on TV or radio, the "to you" does tend to add a bit of a casual and familiar tone; it would rarely be used during very formal communications. For instance, starting an interview with "Good morning to you Prime Minister" is less formal than "Good morning Prime Minister" and would be appropriate only if a familiar tone is acceptable in the circumstance. You can see this by listening to discussions in serious forums (e.g. in a court room, in the United Nations, etc) where the "to you" would be extremely rare.