It was announced in September that Kierston – who plays Kirsty Branning – was one of four faces being axed from the show following the arrival of new boss Dominic Treadwell-Collins.
"It wasn't my decision, it was theirs," the actress told TV Extra. "A new producer came on board and he wanted to shake things up."
Kierston admitted she would have "happily stayed" on the soap but said she was relieved after becoming increasingly unhappy with some of her storylines.
"I always wanted them to make that choice," she said. "I wasn't really happy with where the storylines were going, because I just thought it has become a bit one dimensional."
One plot in particular that Kierston struggled with was when Kirsty pretended to be pregnant to keep her husband Max (Jake Wood) from leaving her.
"I enjoyed a lot of it, but I didn't really believe what I was doing," Kierston added. "In the beginning I did, but I didn't believe the fake pregnancy."
Back in September, the actress hinted that she didn’t plan to remain on EastEnders for very long.
"I'd like to do other projects," she told Digital Spy. "It would be nice to be in the show. Come out, go back in there and come out – I don't know if they're going to allow that, but that would be my ideal situation.
"It would be nice to do film work and dramas, something you can really get your teeth into."