Perhaps it's to warn others about the dangers and wonders he encountered at sea. Also, it could be a way for him to find some sort of closure or make sense of it all himself.
Maybe he wants to share his unique experiences and lessons learned during his journey.
He might tell his story to entertain or inspire people. Or, it could be that he feels a responsibility to pass on the knowledge and wisdom he gained from his adventures.
The ancient mariner tells his story to the wedding - guest.
A mariner might tell his story when he returns home after a long and adventurous voyage.
The ancient mariner tells his story to a wedding guest.
He tells his story when he meets a group of travelers who are interested in his adventures at sea.
Not sure exactly. Maybe around five. But it depends on how you interpret the story and who you consider as the ones the mariner is telling his story to.
He is telling his story to a wedding - guest.
The ancient mariner shares his tale with a random person he meets at a wedding. This person becomes the listener as the mariner recounts his adventures at sea.
He might tell his story to share his experiences with others.
Maybe he wants to share his experiences with others. He could have had some unique or interesting things happen to him that he thinks others can learn from.
Perhaps Hamlet wants Horatio to be the one to spread the truth. Horatio is his trusted friend, and by having him tell the story, Hamlet ensures that the events will be accurately related, free from the misinterpretations that others might impose.