I have read that Michael Trucco was injured in a car accident in 2007. I am assuming that, although he was able to continue in his role on nBSG, his spinal injury prevented him from acting and moving at his full potential and that is why he went into the 'Tub'. (Maybe I am wrong on this last assumption-- I do not know).
I am assuming that the actor's unfortunate injury may have given one/some of the writers an idea of how to shape the course of the developing revelations of the story of the Final Five.
I get the idea that the 'resolution' and ending of the series kind of got made up as they went along towards the end. Has anyone ever heard if there had been a plot line they were following initially that got abandoned in favor of using Anders as they did?