[tel]

Have you ever seen the process transforming a set of lecture notes to a textbook? That process is almost inconceivable for the professor (who has teaching and research engagements) to complete alone. Often they have a lot of help from graduate students, but not always.

Worse, I've read a great deal of math books that were unedited. Arguments end up in the wrong orders, sections are missing, notation changes without notification or regard for readability, numbering fails to match up (not even LaTeX can help if you change your labels midway), figues go missing, indices are wrong, exercises are mislabeled (or accidentally impossible!).

Even with an editorial team there's often a hefty and vital errata for most major textbooks. It's just a lot of organization.

I don't think editors are going anywhere for a long time. The role they serve is crucial. I do totally agree that they don't need to be tied to publishing-as-a-process though.