My theory for the Pirates of the Caribbean:Dead Men Tell No Tales after credits(Ar! There Be Spoilers Ahead! Sail At Your Own Accord)

The movie opens with a boy rummaging around a room with notes about the Flying Dutchman and a trident. The boy grabs a map from his desk and makes his way to a dingy. He rows out a few miles away from shore, looks at his map, then ties a few cannon balls to his ankles. He throws the cannon balls off the side of the boat then jumps into the water. As he sinks farther and farther we begin to see the Flying Dutchman. When the boy lands on the deck of the ship, it begins to ascend to the surface. When it does we see Will Turner come forth and call the boy Henry and it's his son. 

Henry goes on and on about finding a way to break his curse with the Trident of Poseidon. Will urges Henry to not pursue the matter and just live his life away from the sea.
(Fast Forward to the End of the movie)
Henry and Jack break the trident of Poseidon and we see Henry looking at the Flying Dutchman as Will makes his way to land. Will makes it to shore, hugs his son and share this really touching father and son moment. Then we see Elizabeth run up the hill to join them. Will is free from the Dutchman. 

NOW! After the credits we see Will and Elizabeth resting easy on a stormy night. Not long after we see the camera pan down to focus on Will as we hear a familiar lumbering thump of someone walking. The door opens and we see the shadow of a familiar hat. As the figure gets closer to the bed we see more of the shadow and reveals a squirming beard. 

The figure gets close to the bed, Will wakes in a panic, and we see the crab claw of Davy Jones. We see Will wake up, look at the door, look at Elizabeth, and he pulls her close and fall back to sleep in each others arms. The camera pans down an we see barnacles, then the screen goes black.

A lot of people have been troubled by this and think it's a continuity problem. Well here's my theory and hope it may clear some things up.

In the lore of the Pirates universe The Flying Dutchman was created to ferry souls who died at sea to the other side. This is a duty of immense responsibility in this world, not a curse. Now, yes one could argue that only being able to step foot on lad every 10yrs to enjoy the pleasures of the flesh is a curse but the duty must be filled none the less. Also, the duty was not assigned by Poseidon but Clypso (Tia Dalma). So now that Will no longer has to carry the burden of taking care of those who die at sea the Flying Dutchman still needs a captain, but who is to fill that role? No one stabbed Will's heart therefore no one takes his place. Through magic the role reverts back to the one who held it last, Davy Jones. That is why he comes back. People are also wondering why Davy Jones is still transformed and not back to his human form. Well if you remember Tia Dalma talks about the consequences of not performing the duty's of the Dutchman. If you do not ferry the souls you are transformed. I also believe it is a reflection of the soul. Sure people change but you cannot change who you are deep down.

So there's my theory thus far on why Davy Jones is back.