That's odd. I wonder if these people that like looong lines are mostly younger people that have read more from screens than books (but not so young that they've read more from phones than computer screens :))? A book with very long lines would be super weird.

Agreed. I'm specifically referencing wasted space. As I've gotten older, that "wasted" space gets replaced with zoomed fonts using ctrl+=. I've found this attitude and use isn't all that unique anecdotally, so I found the assertion that it's "rare" to be contrary to my own experience. I have no citation the other way though!