"Revenge" came to a close after season four because Emily Thorne, also known as Amanda Clarke, came close to fulfilling her vengeance plan against the Graysons, and therefore the series had hit the mark it needed to end. Additionally, the ratings of the show were dwindling.
Emily had made several people responsible for her painful past pay, and she had even dropped off her alias, revealing that she was Amanda Clarke. Most significantly, her nemesis Victoria Grayson had died, making the ultimate revenge quest a bit challenging. According to the executive producer, Sunil Nayar, the ABC TV show had hit exactly the mark it needed to end. The fourth season also saw the show’s rating in the 18-49 demographics score sink to 1.11 which is the reason ABC decided to bring it to a close.