Board Thread:The Panopticon/@comment-1947484-20130805130556/@comment-4028641-20130805195900

William Hartnell left because of health issues, Patrick Troughton left because he wanted to go out on a high note for both him and the audience, Jon Pertwee left because he wanted to continue his stage carrer and because everyone he had worked with for the last few years were either dead (Roger Delgado) or had left (Katy Manning, Barry Letts), Tom Baker left because he didn't like the direction that the show was going in, Peter Davison left for Typecasting reasons, Colin Baker was straight up fired, Sylvester McCoy's season was cancelled, Paul McGann's season was never picked up, Chris Eccles didn't like the way that people were treated on set (including him), David Tennant didn't want it to start feeling like a job, and Matt Smith still "doesn't know [why]". :)