Will and Elizabeth didn't return for Pirates of the Caribbean: On Stranger Tides because Orlando Bloom and Keira Knightley wanted to pursue other projects. For all the attention Johnny Depp received for his Oscar-nominated performance as Jack Sparrow in 2003's Pirates of the Caribbean: The Curse of the Black Pearl, he wasn't the film's lead(s). That honor went to Bloom and Knightley, who co-starred as the star-crossed lovers Will Turner, a humble blacksmith's apprentice, and Elizabeth Swann, the adventure-seeking daughter of Governor Weatherby Swann. It's unknown if Bloom and Knightley will return for the potential Pirates of the Caribbean 6.

https://screenrant.com/pirates-caribbean-4-elizabeth-will-not-return-reason/