didn't return for the 50th anniversary because of an old feud with the BBC. After agreeing upon his departure that neither Eccleston nor the BBC would comment on the reasons behind it, the broadcaster released a statement claiming that Eccleston was leaving because he was "tired." The actor forced the BBC to retract the statement by threatening to sue, since the implication that he was easily tired harmed his ability to get other roles.
Eccleston has said in his autobiography I Love the Bones of You that he is a lifelong anorexic, and he was struggling with the disease while filming the first season of the Doctor Who revivial. Eccleston departed Doctor Who after that first season, but his version of the character is still fondly regarded by fans despite his short tenure.
Radio Times reports that Eccleston talked about his decision not to return for the Doctor Who 50th anniversary episode, "The Day of the Doctor," at Rose City Comic Con. He said that there were two reasons behind him declining a chance to reprise the role, the first being that "I didn’t feel that what they were asking me to do did justice to the Ninth Doctor." The second reason was that Eccleston was still unhappy with the BBC for attributing false quotes to him back when he originally left the show.
“I liked Steven Moffat a lot. I considered it. But it had an enormous emotional impact on me, what happened with Doctor Who. As the series was going out, as the series was being celebrated I was being vilified in the press in the UK because of the statement that the BBC issued. And it caused quite a depression in me that year. While everybody was going ‘Doctor Who’s great – he’s great and he’s gone’. Because they [the BBC] kind of smeared me and told lies about me."
David Tennant's Tenth Doctor returned for "The Day of the Doctor," but instead of bringing back Eccleston's Ninth Doctor, the episode featured John Hurt as the "War Doctor." The War Doctor followed Paul McGann's Eighth Doctor and preceded Eccleston's version in the show's timeline, and was a darker incarnation of the character who was responsible for ending the Time War by destroying both the Daleks and the Time Lords. Reflecting on that storyline in the show, Eccleston said that his decision not to return actually worked out well:
"The virtue of that is that we then get the War Doctor. Because if I’d have come back you wouldn’t have got the War Doctor – the War Doctor was there precisely because the Ninth Doctor wasn’t. And John Hurt’s a far better actor than me, and that opened up a whole new dimension. So it was a positive thing really."
The current version of the Doctor is played by Jodie Whittaker, who took over the role from Peter Capaldi and will return in early 2020 for the 12th season of the long-running sci-fi show. Perhaps one day the bad blood between Eccleston and the BBC will settle and the actor will return to play the role in a guest appearance. But until then, we'll always have season 1.
Source: Radio Times