The text measure / line length argument probably makes sense for paperback books, and that would likely extend out to mobile/tablet as well.

But perhaps it doesn't make sense when reading on the desktop.

In desktop, you can easily scroll the page to keep track of your spot. You can also use the mouse cursor for to keep your spot in difficult areas. The gains of having long line lengths likely outweigh the occasional difficulty in keeping your spot. The eye reads across faster after all.