Earlier quoted context omitted.
Dictionaries in columns statistically reduce white space and thus reduce the page count. Especially for the definitions that are very short, for example when they only reference a more preferred spelling or a more prominent word that has the exact meaning.
So multicolumn layout increases whitespace in newspapers but decreases it in dictionaries? Funny how it always does the exact thing needed to disprove whatever I say in this exact moment.
You don't really want to reduce the number of sheets for your newspaper because size of the newspaper is an indicator of quality. But trimming off maybe 10% of a dictionary is worthwhile. Size of a dictionary is a quality indicator too, but the absolute production cost is more for a book so saving production costs is more pressing.