Warning: SPOILERS for Star Trek: Picard Season 2's Finale - "Farewell"
Wesley Crusher's (Wil Wheaton) surprise return in Star Trek: Picard season 2's finale retcons Star Trek: The Original Series and explains why Wesley won't appear in Star Trek: Picard season 3. Wesley's was one of the many shocks in Star Trek: Picard season 2's ending; Jean-Luc Picard (Patrick Stewart) and his motley crew set Star Trek's timeline back on its proper course but, in the process, bid farewell to Q (John de Lancie) and Cristobal Rios (Santiago Cabrera), who opted to remain with his newfound family in 2024 Los Angeles. But Wesley didn't interact with Picard, his former Captain. Instead, Crusher came to Earth to recruit Kore Soong (Isa Briones) into the Travelers.
Wesley's destiny was marked to become a Traveler from the very beginning of Star Trek: The Next Generation. The young Crusher first met the Traveler (Eric Menyuk) in the TNG season 1 episode, "Where No One Has Gone Before," which also contains the only canonical appearance of Jean-Luc's mother, Yvette Picard (Herta Ware), before Star Trek: Picard season 2 retconned her backstory. Wesley encountered the Traveler twice more in TNG; meanwhile, Crusher's Starfleet Academy career was marked with scandal because of his role in a cover-up when one of his classmates died. In the TNG season 7 episode, "Journey's End," Wesley left Starfleet and agreed to go with the Traveler to explore new planes of existence in time in space, becoming a Traveler himself. However, Wesley reappeared nine years later in Star Trek: Nemesis, mysteriously wearing a Starfleet uniform with a Lieutenant's rank at the wedding of Will Riker (Jonathan Frakes) and Deanna Troi (Marina Sirtis).
Wesley shockingly returned in Star Trek: Picard season 2's finale to recruit Kore Soong as a Traveler. In doing so, Crusher gave a remarkable download of new information about the Travelers and their galactic purpose. According to Wesley, the Travelers are "very different" from the Q Continuum and their function is to protect the universe's "tapestry" from "annihilation." One of the Travelers' responsibilities is recruiting and dispatching Supervisors to protect people who are crucial to the timeline, such as Tallinn (Orla Brady), who fulfilled her mission to protect Renée Picard (Penelope Mitchell) from Dr. Adam Soong (Brent Spiner). Wesley's revelation of the purpose of Gary Seven (Robert Lansing) and the Supervisors from "Assignment: Earth" answers a Star Trek question that has lasted for 54 years, and Star Trek: Picard's retcon canonically links TOS's Supervisors to TNG's Travelers.
Wesley's appearance in Star Trek: Picard season 2's finale was a secret that was, thankfully, never leaked, which made it a complete and welcome surprise. Wil Wheaton hosts The Ready Room, a behind-the-scenes series that covers all of the Star Trek shows on Paramount+ but when the entire cast of Star Trek: The Next Generation was announced to star in Star Trek: Picard season 3, Wheaton issued a statement that he would not be joining his TNG castmates. Taking Wheaton at his word, Wesley's cameo in Star Trek: Picard season 2 would effectively mark Wesley Crusher's final appearance in Star Trek. It's an update to Wesley's whereabouts that brings Crusher's story to an end while passing the torch to a new Traveler, Kore Soong.
However, this also means that there's no explanation for why Wesley Crusher was suddenly back in uniform in Star Trek: Nemesis. Perhaps Wes took a break from matters of galactic import, returned to Starfleet, and then realized his best destiny is as a cosmic being, after all. Crusher did tell Kore that he made mistakes that affected the galaxy and it's possible there's an inference that briefly leaving the Travelers was one of them. Thankfully, Wesley's quick hello-and-goodbye in Star Trek: Picard gave his classic TNG character a proper closure that nods to Wesley Crusher's importance to Star Trek. Meanwhile, it remains to be seen if Kore Soong will be Star Trek's new Traveler and if she will return as a being who defies time and space in Star Trek: Picard season 3.
Star Trek: Picard Season 2 is streaming on Paramount+.
Star Trek: Picard Season 3 premieres in 2023 on Paramount+.