"Terminator Salvation" flopped primarily due to a combination of factors. Critics and audiences felt it strayed too far from the franchise's roots, lacking the iconic characters and emotional depth of previous installments. It also faced stiff competition at the box office and struggled with a convoluted plot that confused viewers. Additionally, the film's darker tone and focus on action over character development alienated some fans. Overall, mixed reviews and a divided fan base contributed to its underwhelming performance.

"Terminator Salvation," released in 2009, received mixed reviews from critics and audiences. While it had a production budget of around $200 million, it grossed approximately $371 million worldwide, making it financially successful but not a blockbuster hit in the way its predecessors were. The film was criticized for its plot and character development, which contributed to its divisive reception. Overall, it can be considered a moderate success rather than a definitive hit or flop in the franchise.

Arnold Schwarzenegger did not appear in "Terminator Salvation" because the film is set in a post-apocalyptic future, focusing on the war between humans and Skynet's machines. At the time of production, Schwarzenegger was not involved due to his role as the Governor of California. Additionally, the filmmakers opted to use a digital recreation of his likeness from the original films for a brief cameo, but ultimately, they decided to focus on new characters and storylines rather than featuring Arnold's iconic T-800 character.

"Terminator Salvation" is not a direct sequel to "Terminator 3: Rise of the Machines." Instead, it is set in a post-apocalyptic future, specifically in 2018, focusing on the battle between humans and Skynet's machines. It serves as a reboot of the franchise's timeline, exploring the events leading up to the war against the machines, rather than continuing the story directly from the previous films. While it follows the same overarching narrative of the Terminator series, it shifts the focus to a new storyline within that universe.