As an outsider to the specific subjects of the theses concerned, I
have always understood the purpose of an introductory chapter to be
to demonstrate the writer's awareness and understanding of existing
literature and knowledge in the field, to raise any appropriate
methodological issues, and to show the justification for the thesis
topic and how it fits into the wider field.
This seems to me to justify continued insistence, even - or perhaps
especially - by experts in a topic on a substantial introduction