[jesus_666]

It's an implementation of an old recommendation to never have more than 80 characters per line, ostensibly to limit horizontal eye movement but mostly stemming from legacy 80-character terminals and punch cards.

The value of that recommendation is rather dubious considering today's high-resolution displays that allow for smaller font sizes. 80 readable characters at 768p are not the same as 80 readable characters at 4K.

[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.

[the_other]

As someone who uses screen zoom tools constantly, I vote in favour of the 80ch column width recommendation. If you want to support extra wide monitors, consider using multiple columns, rather than a single, wider one.

[crote]

Multiple columns don't really work with websites, as web content almost always going to be vertically scrollable.

Columns work great for things like a navigation sidebar or an image grid, but it just doesn't play nice with long-form blog content.

[CyMonk]

It actually goes back to mechanical typewriters, which were limited to 70 to 90 characters per line. Commonly used punch cards also had 80 columns. Both were the inspiration for the 80 characters in computer terminals.

[rsolva]

Weeel, actually! ... It dates back to the early days of the printing press, and has been a general convention since then.

Rules can be broken, but not without consequence.