I was interested in the way you try to separate need from motivation. I’d like to question this further.
Surely the progession is:
want to work at a uni —> need a doctorate —> do this course = extrinsic motivation
The need is predicated on the desire to work at a uni, to be of that status. This is a motivation and logically comes before the need to have the doctorate degree. If there was no in/ ex trinsic desire to work at a uni (can’t separate that without knowing inside the individual’s head), there’d be no pressure to have the degree. So, I agree with Wolfgang that motivation is a key element here.
I think that you are right about there being other ways of attaining practical knowledge. However, this particular format of having to respond daily to others’ essays, the writing of the essay weekly, the continued readings, the group work, the SPSS expectation (it’s always visible in the left menu), and so on; these together provide a training that I don’t think is available outside of a doctoral level course. Of course, we can learn, for example, advanced stats on a MOOC (I did last year) and build up our skill set piece-by-piece, but for me, it’s the daily expectation that is the single biggest element in our growth.