Agents of SHIELD's creators explain why Fitz was missing for the most part of the show's final season. As Marvel TV's inaugural project, the recent ending of the ABC series also marked the end of an era for the supposed small screen branch of the MCU. While the story further diverged from what Marvel Studios was doing on the big screen, it remained popular, with the show tackling some of the finest character arcs in the universe. With a solid team coming into season 7, fans were excited to see Phil Coulson, and his whole gang for one last mission - so it was quite disappointing that Fitz was absent for the most of it.
Like Joe and Anthony Russo's Avengers: Endgame, Agents of SHIELD's final season utilized time travel. It premiered with the team in the middle of the Great Depression as they tried to stop the Chronicoms' attempt to keep an important ingredient of the Super Soldier serum from Dr. Abraham Erskine which would've resulted in the Super Soldier program, HYDRA, and Captain America not coming to be. The show also abided by the time travel rules stated by the Ancient One to Smart Hulk, which paved the way for the plot twist towards the end of the show - apparently, the gang was actually in a different timeline, while Fitz remained in the main universe.
It was a nifty reveal which also let Agents of SHIELD still keep Fitz at the heart of the story without the need for his physical presence in the early episodes. This creative decision, however, wasn't something that the show creators originally wanted as they explained in a new interview with TVLine. As it turns out, they had very limited time with Iain De Castecker so they had to be smart with how they're going to use him in the story.
Jed Whedon: “Some choices aren’t made by us. So we did what we could, and we tried to make it rewarding with the pieces [we were given]. Sometimes it’s 3D chess.”
Maurissa Tancharoen: “To be clear. Iain is an exceptionally talented actor and one of our dearest friends. It was just it was time for him to go [and] explore new things.”
Outside of Agents of SHIELD, De Castecker has been working on other projects including the mini-series titled Us - a BBC adaptation of David Nicholls' book of the same name, as well as, the short film Upstairs. While this resulted in his minimal appearance in the ABC/Marvel show, the series' showrunners argue that it's all for the better as it has resulted in a much more impactful pay off when they finally revealed where he was and what was actually going on in Agents of SHIELD's last season. They also pointed out that Fitz's absence brought “Simmons and [grandson] Deke closer together.”
While Agents of SHIELD's final season didn't have a lot of Fitz and Gemma Simmons' moments, the series made up for it by giving them their much-deserved happily after. Overall, while fans would've loved to see Fitz carrying out the mission on the ground with his team, him staying back and monitoring everything that was happening from the primary timeline ensured that he was involved throughout. Admittedly, it's also a much smarter and safer move compared to all the Avengers traveling through history via the Quantum Realm in Endgame without leaving anyone to man the HQ and make sure everything's going according to plan.
Source: TVLine