here is a sample
The interests of academics and universities on the one hand and PhD students on the other are not well aligned. The more bright students stay at universities, the better it is for academics. Postgraduate students bring in grants and beef up their supervisors’ publication records. Academics pick bright undergraduate students and groom them as potential graduate students. It isn’t in their interests to turn the smart kids away, at least at the beginning. One female student spoke of being told of glowing opportunities at the outset, but after seven years of hard slog she was fobbed off with a joke about finding a rich husband
For my own research (into potential for graduate students to form co-operatives as a service provider) I just obtained the much cited (and also bleak) book , Leaving the Ivory Tower: The Causes and Consequences of Departure from Doctoral Study (by Barbara E. Lovitts).
For me, the hardest departures I see are where the student has made a huge sacrifice, for many years, to attend grad school, but at the end of their program it doesn't work out. In my experience there are usually several factors piling up against the student, many of them also outside the university's control, and little means to help the student find their way through if those external problems cause long delays.