Perhaps this is because his book was originally a doctoral thesis and it has not fully shaken off the shackles of its original form.
The Times Literary Supplement (2013)
He gained first-class honours in history in 1933 and held a research fellowship while writing his doctoral thesis.
Times, Sunday Times (2009)
The film lacks rigour but it is a TV show, not a doctoral thesis.
Times, Sunday Times (2010)
It introduces a man who is heavily involved in practical political administration in Toulouse, while pursuing his career as a teacher and completing his doctoral thesis.