When actors such as Holmes are busy with other things — a Scientologist husband, a new baby, a new career direction — that also can be a reason to want to make a switch.
During an interview earlier this year with MTV News for "Mad Money," the comedy Holmes opted to star in rather than "The Dark Knight," the 29-year-old actress said she had no regrets turning down the role of Rachel Dawes.
"I had a great experience working with Christopher Nolan [and] I'm sure it's going to be a great movie," she said. "I chose to do this movie ['Mad Money'], and I'm really proud of it. I was so excited to work with Diane [Keaton] and Queen Latifah and [director] Callie [Khouri]. It was so much fun to create this character. I wish them the best for the summer. I'm excited to see it."
"Mad Money" earned $20.7 million at the box office.
Stepping into a supporting role certainly is easier than taking on the weight of established franchises, often with Oscar-winning performances.
Such was the case when Julianne Moore took on the role of Clarice Sterling in 2001's "Hannibal," perfected by Jodie Foster's Oscar-winning performance 10 years earlier in "The Silence of the Lambs."
Zacharek acknowledged that replacing an actor in an established franchise would be a challenge for any performer.
"You have to be proprietary of any role you take on. You're the one who's going to be hung out to dry if it doesn't work," she said. "I imagine it's a difficult thing, maybe more so with Julianne Moore and Jodie Foster. You're kind of stepping into her shoes, whereas with something like the Bond character — nobody wants to be the worst Bond."
But changing the lead actor in the 007 franchise is to be expected, said Box Office Mojo's Gray.
"That's how they reinvigorate the franchise," he said. "It's about the character and the overall story line rather than the actor."
Choosing a new Bond is no easy task. Some fans of Roger Moore and Sean Connery never truly grew to embrace Pierce Brosnan.
The "new" Bond, British actor Daniel Craig, underwent an online thrashing when he was chosen to play Agent 007, even inspiring the Web site www.danielcraigisnotbond.com. But his first outing as the dashing secret agent in 2006's "Casino Royale" changed many naysayers' minds.
Salon's Zacharek also was originally skeptical when Craig was cast, describing him as "scrappy ... a street cretin Bond."
But then "I fell in love with him," she said. "He takes the basic template and brings something to it," including looking great in a suit and lots of physical action.
"That's what an actor has to do. You don't want to be disrespectful, but you do have to look at the foundation and see what you need to take of the previous characterization," Zacharek said. "I don't think there's any other way."
While Bond has a history rooted in lead-character changes, the Jack Ryan franchise, based on the best-selling Tom Clancy books, has more to do with the actor in the role. After Alec Baldwin abandoned the franchise following "The Hunt for Red October," in 1990, the studio instead used Harrison Ford's popularity to market the next films, 1992's "Patriot Games" and 1994's "Clear and Present Danger," Gray said.
"The Jack Ryan character doesn't have as much stock as a Batman or a Bond," he added.