I got my Ph.D. from a US university with such a style guide now nearly 25 years ago. It annoyed me so I asked, in polite fashion.

The answer I received was a sensible historical reason. Ph.D. theses would historically be microfilmed and distributed to libraries and other interested parties as microfilm, or printed on paper from microfilm. This was done through a single provider, UMI (University Microfilms International).

Dissertation offices developed standards in response to legibility issues that arose through this process, in particular font size and margins due to limitations of the to-microfilm and from-microfilm process, as implemented by UMI. Those standards have stayed due to inherent conservatism, even though in this electronic-pdf age they seem rather obsolete, and were already obsolete 20+ years ago.

I personally experienced that if an old Ph.D. dissertation reprint had something illegible, you would write a letter to the Ph.D. institution's dissertation office, and they would send an individual to the library or archive, wherever the original dissertation was kept. There they would take a good quality photocopy of the page and mail it to you. I expect any such task could easily translate to tightening the dissertation formatting requirements so that it didn't happen going forward.

I asked but didn't get a satisfactory answer about double spacing and obligations on word-wrap and justification, which I felt were particularly annoying and unnecessary. I hazard a guess that interspersed with fully rational and reasonable conditions on resolution/legibility were added other prescriptive standards borrowed from when people actually wrote typewritten manuscripts for University department "working papers" series or similar, that were photocopied and distributed. And from literary agent and publisher historical manuscript submission guidelines, from times when manuscripts needed space for editors and agents to handwrite comments and corrections. But that is my speculation.

I got my Ph.D. from a US university with such a style guide now nearly 25 years ago. It annoyed me so I asked, in polite fashion.

The answer I received was a sensible historical reason. Ph.D. theses would historically be microfilmed and distributed to libraries and other interested parties as microfilm, or printed on paper from microfilm. This was done through a single provider, UMI (University Microfilms International).

Dissertation offices developed standards in response to legibility issues that arose through this process, in particular font size and margins due to limitations of the to-microfilm and from-microfilm process, as implemented by UMI. Those standards have stayed due to inherent conservatism, even though in this electronic-pdf age they seem rather obsolete, and were already obsolete 20+ years ago.

I personally experienced that if an old Ph.D. dissertation reprint had something illegible, you would write a letter to the Ph.D. institution's dissertation office, and they would send an individual to the library or archive, wherever the original dissertation was kept. There they would take a good quality photocopy of the page and mail it to you. I expect any such task could easily translate to tightening the dissertation formatting requirements so that it didn't happen going forward, leading to accretion of picky requirements over time.

I asked but didn't get a satisfactory answer about double spacing and obligations on word-wrap and justification, which I felt were particularly annoying and unnecessary. I hazard a guess that interspersed with fully rational and reasonable conditions on resolution/legibility were added other prescriptive standards borrowed from when people actually wrote typewritten manuscripts for University department "working papers" series or similar, that were photocopied and distributed. And from literary agent and publisher historical manuscript submission guidelines, from times when manuscripts needed space for editors and agents to handwrite comments and corrections. But that is my speculation.