Ninth Doctor actor Christopher Eccleston elaborated on his decision not to return for the Doctor Who 50th anniversary special and claimed that his absence made the story better. 2005 saw the return of Doctor Who after its cancellation in 1989, with doubts amongst the general public that what was remembered as a silly low-budget sci-fi show would have a place in the modern landscape of television. Season 1 of Doctor Who's revival almost immediately disproved all of these notions via well-written, dramatic scripts, modern production values, and an incredibly strong lead performance from Eccleston as the Ninth Doctor.
Eccleston signed onto Doctor Who after being impressed enough with Russell T. Davies' prior written work to take on the role of the time lord, despite not having been a fan 0f the original series. Eccleston was quickly accepted into the hearts of classic fans and the new generation discovering Doctor Who, as his brooding, damaged incarnation spent the season recovering from the effects of the Time War, bringing him back to a wide-eyed traveler of time and space. Despite the reception, Eccleston quit the role after one season for reasons related to how the production was run and the treatment of certain crew members. Since then, Eccleston has re-embraced the part by starring in full-cast audio dramas from Big Finish and appearing more frequently at fan conventions.
When speaking at Supernova Comic Con in Melbourne (via @whittckers) Eccleston was asked about the topic of multi-Doctor stories which led to discussion of his absence in the 50th anniversary special, "The Day of the Doctor." When asked if there were any Doctors he would want to collaborate with in the future, Eccleston laid out his honest thoughts that he considered the traditional multi-Doctor specials to be somewhat creatively bankrupt. He then brought up the fact that he was invited back for the 50th and claimed that his refusal to return actually improved the story as it necessitated the invention of the War Doctor, played by John Hurt. Read his quote in full below:
"No, I've never been a fan of multi-Doctor stories. You know, when I worked on the series I had really strong ideas [...] about what works and what doesn't and I always think that multi-Doctor stories are a bit of a cash in and a bit of exploitation. Creatively, they never worked for me. I looked at the script for the 50th anniversary and I felt as soon as I said I wasn't doing it, it got better. But, you know, the creation of the War Doctor introduced a whole new facet to the canon"
Fans who wanted Eccleston to return in the 50th anniversary special will likely disagree with his comments as it was fairly clear, even before behind the scenes politics were revealed, that the story was written with him in mind with Hurt's War Doctor being a last minute replacement. However, the actor may be right in how his omission made the story more interesting by introducing a brand new Doctor into the pantheon who, due to his participation in the Time War, was a source of conflict from the Tenth (David Tennant) and Eleventh (Matt Smith) Doctors who looked back on him in shame. It's hard to imagine the script would've had this storytelling conflict with Eccleston as there would likely have been a natural impulse to treat his character with reverence and affection, as opposed to Hurt's Doctor, whom the audience has no prior attachment to.
Eccleston's general opinions on multi-Doctor stories once again seem to quell any hopes for a return in the upcoming 60th anniversary. This was always doubtful though since it was announced that Davies would be returning as showrunner from the 60th onwards, along with several key figures from the early seasons of modern Doctor Who, who Eccleston would've inevitably butted heads with. However, Eccleston's engagement with the fans and with the show's mythology in this quote shows that Doctor Who is still an important part of his career to him and that he'll continue to bring new solo audio adventures for the Ninth Doctor, much to the fanbases delight.
Source: Supernova Comic Con (via @whittckers)