Why are footnotes expensive for publishers to reproduce? According to the Purdue OWL APA guide:


  APA does not recommend the use of footnotes and endnotes because they are often expensive for publishers to reproduce.


Perhaps this question belongs on a printing SE, but what could make footnotes expensive? Is it because it will take longer to arrange the small letters on a letterpress?
thank you @user2768; your comment is excellent:

Steven Krantz writes "in mathematics we do not usually put bibliographical references in footnotes (however...it was fairly common in mathematics one hundred years ago). This habit came about in part because typesetters objected to the expense and trouble of typesetting copious footnotes. With the advent of TEX, that particular objection is moot. However, the rule persists." -- arxiv.org/abs/1612.04888 Perhaps APA does not recommend footnotes for historic reasons too.