I did my brief gig with Modern Philology in 1997-98, in the days before the publishing process had gone full-bore electronic. In retrospect, putting together a finished manuscript for the printers was awfully cumbersome...
1. To begin with, many academics in the humanities were still unacquainted with/skeptical of this newfangled thing known to the Kids on Their Lawn as "e-mail." Similarly, you couldn't count on departments having their own webpages ("what are those?"). This could make it difficult to ask queries on short notice--or issue pointed reminders about overdue book reviews--especially when you were working with an author across the pond. (It also made life painful when you were trying to find reviewers' addresses, especially English reviewers who published under one name and were listed in directories under another!)
2. Checking an author's quotations meant walking from Wieboldt Hall over to the Regenstein Library and wandering through the Reg's somewhat bizarre arrangement of stacks. I liked the Reg, and I liked the stacks, but I did not necessarily like having to walk over there when it was the middle of winter and zero degrees Fahrenheit. Ah, the joys of GoogleBooks and archive.org!
3. Distributing manuscripts to authors involved numerous sacrifices to the relevant divinities. They had to go out, come back, go out again, and come back again, hopefully without disaster. On occasion, disasters occurred, leading to much wailing and gnashing of teeth (and, potentially, a very large hole in the journal issue).
4. You had to pray that authors followed directions, lest the Typesetting Gods become irate and send out Thunderbolts of Doom. When authors did not follow directions, you wound up with things like the Man with the Red Pen. Even when authors did follow directions, there was an unseemly amount of erasing involved.
5. One word: handwriting.
6. Two more words: illegible comments.