* Contractual Disputes: Carpenter's contract was up for renewal at the end of season 3, and negotiations between her and the studio, 20th Century Fox, reportedly broke down. The reported sticking point was salary: Carpenter wanted a significant raise, but Fox was unwilling to meet her demands.
* Creative Differences: While not explicitly stated, there were rumors of tensions between Carpenter and the show's creator, Joss Whedon, over the direction of her character, Cordelia Chase. Carpenter has since spoken out about feeling "marginalized" and "disrespected" during her time on the show, which could have contributed to her decision to leave.
* Seeking New Opportunities: Carpenter may have also felt ready for a new challenge. After three seasons, she was seeking a chance to explore other acting roles and opportunities outside of "Angel."
It's important to note that there are different perspectives on this situation. Some people have defended Whedon and Fox, while others have expressed support for Carpenter. The truth likely lies somewhere in the middle, with a complex interplay of factors leading to Carpenter's departure from the show.