Narrow columns are easier to mark up with a pen for editing and note-making purposes. On the other hand, I have often wondered why this convention was used so

Narrow columns are easier to mark up with a pen for editing and note-making purposes. On the other hand, I have often wondered why this convention was used so much, especially when some types of content would never reasonably fit into a single column (and people didn't want to float a graphic in there) What sort of tablet are you using in 2020 which doesn't have the pinch-to-zoom functionality? "two columns to squeeze it all in" Just use a single column and half the pages then...