Why did Frodo have to leave the Shire after the ring was destroyed?

Two years after the Ring was destroyed, Frodo as the Ring-bearer and Bilbo as the Ring-finder were accorded the special right to travel to Valinor — where Frodo might be healed and find peace — together with Gandalf, Elrond and Galadriel, the Keepers of the Three Rings. They boarded a ship at the Grey Havens and passed over the sea. Having no children of his own, Frodo left his estate, along with the Red Book of Westmarch, to Sam, who, according to Hobbit legend, followed Frodo across the sea sixty-one years later, following the death of his wife Rose Cotton.

Why did Frodo have to leave the Shire after the ring was destroyed?
The wound he received from the Nasgul poison blade in The Fellowship of the Ring never healed so he was going to Valinor because it was the only place he could be healed...if he had stayed in the shire the poison would have slowly killed him.
Reply:Thank you for such a great question! And Thanks also to all the great answers I've read so far. Obviously, I'm not the only one who is a serious student of Tolkien.
Reply:The time of magic was at end and the World was moving into the age of man. When Frodo became a "Ringbearer" he became a part of the world of magic, so there was no place for him in the new world.
Reply:They had seen to much. That world was no longer the place for them.
Reply:All of the remaining ring-bearers had to leave. The magical forces of Middle Earth pretty much went to valinor to retire, and since Frodo and Bilbo were both tainted, they had to leave too.

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