By “Smallville” season 6, the show had outlasted its original network, the WB. The CW was created from a merger between WB and the UPN, so that’s where the final half of “Smallville” aired. Then, after season 7, Rosenbaum, Kreuk and series creators Alfred Gough and Miles Millar departed the series. (The final three seasons saw previous writing teams, Todd Slavkin & Darren Swimmer and then Kelly Souders & Brian Petersen promoted to showrunners.)
In a 2021 oral history of “Smallville” at the Hollywood Reporter, all four said they felt it was time to move on. Gough recounted:
“[Millar and I] had done seven seasons of the show. They [the network] wanted to keep going sort of indefinitely. We knew it was going to go further than season 8. We had told the stories that we wanted to tell. The show would keep going. We had trained all the people who were there that went on to run it. ‘OK, we think the best thing for us and for the show is for us to step aside and let someone else do it.'”
Rosenbaum said: “I didn’t leave the show. I had a six-year contract and I ended up doing seven years. And so I felt like I had done enough and the character [of Lex] had done enough.” Kreuk also added that she had started “Smallville” when she was 18 and, when she left, she was 26. “[‘Smallville’] had been my entire young adult life. I didn’t know what the stories for Lana would be in the future. I didn’t want to live in a love triangle forever. I hate playing love triangles, and I just wanted to explore other aspects of my life,” Kreuk said.
For their part, Gough and Millar have admitted they probably dragged the Clark/Lana story on for too long, which itself could be a symptom of the show lasting longer than they had expected. On an episode of Rosenbaum’s “Inside Of You” podcast featuring Gough and Millar, the three of them all reiterated that by “Smallville” season 7, they were burnt out. Then, at the beginning of “Smallville” season 10, the entire original cast besides Tom Welling himself had left. (Allison Mack, who played Clark’s friend/Lois’ cousin Chloe Sullivan, stayed on in a reduced recurring role during the final season.)
Despite Gough and Millar’s departure, “Finale” wrapped up the show the way they’d planned too. In a 2011 interview with Collider a few months before “Smallville” ended, Millar said: “The last moment of the show would be [Clark] putting on the [Superman] suit and flying off into his future and his destiny. That was always in our heads. That would be the ultimate end to the show.”
True enough, “Finale” ends with Clark ripping off his shirt, Christopher Reeve style, to reveal the Superman suit underneath and then flying off to help people in need.