[trashb]

The 50-70 CPL is, in general, just well suited to reading. This has been researched, and by quickly searching I can find the following (beautifully layed out) paper: https://journals.uc.edu/index.php/vl/article/view/5765

To my surprise the paper actually concludes that fast readers prefer shorter line length.

Edit: Usually books and newspapers are also more or less in compliance with this convention and those where around since before computers where a thing.