[KC8ZKF]

Terminals were commonly 80 characters wide, which doesn't explain anything. Why were terminals commonly 80 characters wide? Perhaps terminals were commonly 80 characters wide because punch cards were commonly 80 characters wide, which doesn't explain anything.

Eighty characters is the "standard" limit for code width because eighty characters is the "standard" limit for code width.

[wdr1]

It doesn't explain everything, but it does explain quite a bit -- notably it traces the history of the standard back to punchcards.